By S. Connor. University of Louisville.
Black arrows indicate the direction of flow of fluid move Collecting lymphatics are tubular and larger lymphatics buy sildalis 120mg on line. Lymph flow is further facilitated by skeletal muscle con- interconnected lymph vessels and then from these traction discount generic sildalis uk, negative intrathoracic pressure (during inspi- vessels into tubular lymphatic vessels and the larger ration) cheap sildalis 120 mg with amex, and suction effect created by higher velocity of lymphatic vessels (Fig. Substances that increase lymph flow are called lym- lar to that of smooth muscles of blood vessels. It is formed by Types of Lymphatics transcapillary exchange and exchange between tissue fluid and lymphatic ducts. Lymph flow is much slower Lymphatics are of two types: Initial lymphatics and collect- (1 mL/min in thoracic duct) than blood. Presence of more lipid Initial Lymphatics gives milky color to the lymph, hence called chyle. Initial lymphatics are lymphatic bulbs and interconnected Functions of Lymphatic Circulation vessels (lymphatic capillaries). Extra amount of fluid left in the tissue space by capil- several ways: lary filtration is taken up by lymphatics and returned 1. No fenestrations in endothelium (non-fenestrated) tribute to water content of plasma to some extent. In liver and intestine, a significant quantity of protein absent enters into interstitial space. This protein is returned Initial lymphatics lack valves and smooth muscles in to circulation via lymphatics. Tissue fluid enters into them through gaps or 50% of circulating protein in the blood. Thus, lympha- loose junctions between the endothelial cells present in tics maintain protein content of plasma. Mononuclear phagocytes in lymph nodes remove bac- the active phase of the disease process. Enlarged lymph nodes teria and pathogenic organisms from lymph draining (lymphadenopathy) in a particular part of the body provide clinical clue to the physician to locate the site of infection. Thus, they play protective function submandibular lymph glands indicate infection in the throat (Clinical Box 18. Lymph node, spleen and associated lymphatic tissue are secondary lymphoid organs where the lymphocytes reside and mature. Splenomegaly and lymphadenopathy indicates infection or proliferation of abnormal cells in general. Functions of thymus, functions of spleen, composition and functions of lymph, & lymphatic circulation may come as Short Questions in exams. In Viva, examiners may ask… hormones secreted from thymus, how T cells are developed in thymus, functions of thymus, spleen and lymph node, composition of lymph, and design of lymphatic circulation. Name the primary and secondary lymphoid organs and outline the general principles of immunity. Give the physiological basis of rejection of organ transplants and the prevention of its rejection. List different types of immunotherapy and describe importance of monoclonal antibodies in immunotherapy. The specific defense mechanisms of the body are col- ments that threaten our normal health is the immunity. The immune responses greatly depend on the site of such as bacteria, viruses, fungi, protozoa and multicellular infection and the type of infecting organism (patho- parasites. Therefore, the living beings require quick and continuous mechanisms to kill and remove the the ability of the body to defend against invading agents is pathogens from their body. Recognition of pathogen or the foreign material, mechanisms that can broadly be divided into specific 2. Acquired (adaptive) immunity set of lymphocytes are activated with specific antigens 1. Passive immunity (transfer of antibody from mother) (Innate Immunity) – Ig G via placenta – Ig A via breast feeding Non-specific defense systems include the skin and mucous 2. Artificially acquired membrane (mechanical factors and chemical factors), anti- a. Active immunity microbial mechanisms (interferons and complements), natural killer cells, phagocytosis, inflammation and fever. Defense by inflammation and fever Largely, immune responses are of two types: Mechanical Defense 1. Skin and epidermis: Skin and epidermis are the most important and natural defense barriers of the body. They Scientist contributed form the partition between the body and the external Paul Ehrlich a German physician and scientist environment that immediately checks the entry of orga- worked in the fields of immunology, and antimicro bial chemotherapy. He was awarded Nobel Paul Ehrlich surface, mucous membrane covers the body, especially Prize in Physiology or Medicine in 1908 for his (1854–1915) the surface of body cavities such as oral cavity, nasal cavity pioneering work on humoral immunity. Mucous membrane mechanically traps the organisms Innate immunity: Innate immunity is mostly nonspe- and secretes chemicals that inhibit the organisms. Mucus, by virtue of its physical pro- cytokine and antibacterial peptides from phagocytes perty traps microorganisms, especially in the respiratory, and inflammatory cells, activation of complement sys- gastrointestinal and genitourinary tracts. Hairs: Almost all openings (entry points) of the body Scientists contributed such as nostrils, ears, eyes, anus, urethra and vagina (in females) are guarded by hairs. Bruce A Beutler Jules A Hoffmann Ralph M Steinman Tear: Tear is secreted from lacrimal apparatus. It the Nobel Prize in Physiology or Medicine 2011 was divided, with washes the microbes and dilutes the chemical substances one half jointly to Bruce A Beutler and Jules A Hoffmann for their produced by microbes. They are present in the spleen, lymph nodes, bone Defecation: During the act of defecation, fecal matter marrow and blood. Osmotic lysis by incorporating perforins into the sur- stances like unsaturated fatty acids that kill microbes. They release interferons that activate phagocytosis stances like lysozyme secreted in saliva, tear, sweat and and immunity. They possess Fc receptors that allow them to kill anti- of gastric secretion kills many micro-organisms and also body coated viruses. Kill by antibody-dependent cell-mediated cytotoxicity tion also prevents entry of microbes into the body. They do not require prior sensitization to kill micro- destroying the organisms by facilitating opsonization and bes. They have the ability to kill a wide variety of micro- Role of Granulocytes and Mononuclear Cells organisms and tumor cells. There are two types of macrophages: the wandering macrophages and fixed macrophages. Mechanism of phagocytosis includes chemotaxis, margi- nation, adherence, ingestion, and digestion and killing (For details, refer “Neutrophil” Chapter 17, Figs. Kupffer cells of the liver In the process of inflammation, microorganisms are killed b.
A thin coat of gel may be utilized to ment buy sildalis 120 mg free shipping, with patients noticing continual improvement buy 120mg sildalis free shipping. Immediately after treatment there which is most noted in darker skin types discount sildalis 120 mg mastercard, particularly is moderate erythema and slight edema and duskiness of East Asian skin types (Fig. Short-term complica- (Gentlewaves) is performed immediately posttreatment tions include acne fares, edema, erythema and peeling, to reduce posttreatment edema and erythema. Even though multiple treatments are necessary, devices can deliver excellent results with enhanced 182 V. Narurkar Before 1927 treatm ent Im m ediately post 1 day post 2 days post 3 days post 4 days post 5 days post 1 week post Fig. Our antibiotic with a history of adnexal disease– such as morphea, of choice is azithromycin (Z pack) to start the day scleroderma and other connective tissue disorders, before the procedure and continue for 3 days. Treatment with oral antibiotics remains cial areas such as the neck and chest are treated, controversial – we routinely treat patients with oral extreme caution is advised. Technique is key for all antibiotics in the pre- and posttreatment period, as areas, to avoid bulk heating which can produce adverse 15 Fractional Laser Resurfacing 183 Fig. Aggressive emol- liation with petrolatum-based products such as aquaphor are recommended until reepithelialization is complete. Common short-term adverse effects include crusting, weeping, erythema and edema, 15. If this is done, the Thermage treatment is skin resurfacing, they are limited for certain aspects of performed frst, followed by Fraxel. The combination facial aging such as dynamic rhytids, volume loss and approaches allow for synergy of these modalities. Narurkar considerably safer than traditional ablative laser resur- facing and both offer greater recovery and fewer short- and long-term side effects. Combination therapies with botulinum toxins, dermal fllers and radiofrequency complete the picture of fractional laser resurfacing with synergistic effects. Laubach H, Tannous Z, Anderson R et al (2006) Skin responses to fractional photothermolysis. W anner M , Tanzi E, Alster T (2007) Fractional photother- molysis: treatment of facial and nonfacial cutaneous photo- damage using a 1550 nm erbium doped fber laser. Ablative fractional laser resurfacing is indi- cated for more severe photoaging and best suited for lighter skin types and facial skin. Resurfacing lasers (traditional or frac- periorbital wrinkles and rhytids in November 2002. However, longer its clearance to treatment of all skin surface wrinkles duration of recovery, scarring, pigmentary changes, and rhytids. Although there are a growing number of and other complications are more common with surgical other devices and technologies available for nonabla- and ablative procedures due to the very nature of these tive skin tightening, none of these have the accumula- treatments. As a result, noninvasive methods have tion of published studies reporting effcacy compared become increasingly popular, and there is signifcant to Thermage [1–38]. In addition, Thermage treatment demand for effective, proven methods of nonablative protocols have had time to evolve through several gen- skin rejuvenation. Current fows from the device via the treatment tip, through the skin and out through a grounding pad applied to the patient. The treatment is best suited to address Blepharoplasty Percutaneous suture techniques deeper rhytids (such as the nasolabial folds and mari- Nonsurgical treatments onette creases in the face), rather than fne, superfcial Chemodenervation crepe paper type wrinkles along the skin surface. This Tissue fllers relates to the epidermis being protected during the Intense pulse light and nonablative lasers treatment (fne skin surface wrinkles and dyschromias M icrodermabrasion and superfcial chemical peels are best treated by fractionated or more traditional ablative methods of skin resurfacing). Patients must understand obtain a theoretical antiaging beneft from collagen that dramatic surgical or ablative type results are not stimulation in the skin. Patients must had a surgical lift may beneft from this maintenance also understand that although there is some initial con- effect. It is the senior author’s experience that patients tour change, skin texture and tone will continue to with thinner skin typically achieve a more dramatic improve gradually for several months after the treat- result. Depending on each patient’s individual biology require more than one treatment session. Adequate periprocedure patient and depends on energy delivery based on tissue counseling is a key component of ensuring patients’ resistance rather than absorption of laser light energy, satisfaction with the procedure [4, 10]. They are Implanted medical device designed for single use per patient, and are electroni- (pacemaker, defbrillator, etc. Other Thermage system disposable item Relative contraindications costs are listed in Table 16. Dermatologic conditions Collagen-vascular or autoimmune diseases Impaired collagen production (radiation, metabolic, etc. The with appropriate temperament are able to tolerate provider is typically seated on a supportive surgeon’s treatment using oral narcotic analgesics (oxycodone, stool. Topical anesthetics treated clean and free of any makeup or other skin care are counter productive as they numb the epidermis product. If hair bearing skin is to be treated, it is best if and the cooling sensation, but are not effective in the hair is shaved or trimmed in advance. An ini- deep tip is suited for large surface area procedures on tial test pulse is performed prior to beginning treatment the body (abdomen, fanks, arms, buttocks, thighs) – to allow the machine to calibrate skin resistance. The use of the treatment grid gen cooling unit is seen on the left, the ergonomic treatment hand to guide delivery of each treatment pulse is depicted in the inset Table 16. For instance, when making the next pass over the same area, the inter- when treating the face, lower energy (44–61 J/cm2) is section of the grid lines is used. One or tightening, erythema of the skin, and excessive patient two initial passes are performed to cover the entire discomfort are all subjective clinical endpoints of treat- treatment area to achieve uniform contraction of the ment for each specifc area on the skin. Additional shrinkage and defnition In the face, superior and lateral vectors are targeted to can be accomplished by targeting the fbrous septae in lift, tighten and stretch the skin around the lips, naso- this 3-dimensional Z plane. This strategy works well in labial folds and marionette creases, similar to a surgi- areas of fullness such as the submental and jowl regions. Stacking of treatment pulses on top of each other without 16 Capacitive Radiofrequency Skin Rejuvenation 193 Table 16. The total number of treatment pulses required for Results are most impressive in patients with thin skin different zones of the face and neck are tabulated in and moderate laxity. It is usually not nec- lifting of the skin peaks a few weeks after treatment essary to treat skin that is densely adherent (over the and continues for 4 months or longer, as a result of nasal dorsum, ear, and scalp for instance). Upper lid skin is distracted onto the orbital rim and Contour changes seen in the face typically include away from the globe prior to treatment when using the 2–4 mm of brow elevation, smoothing of the nasola- medium depth tip, although the eye lid skin can be bial folds and marionette creases, and better defnition treated directly with the superfcial depth treatment tip of the jaw line and cervicomental angle (Fig. Intrinsic characteristics of the skin such as pore size, acne, and tone are also improved [2, 16, 17]. Collagen stimulation in the skin may If other complementary procedures are to be done con- also provide a theoretical antiaging beneft by replen- currently (Table 16.
Masugi nephritis is an experimental model of Goodpasture syndrome α2 macroglobulin (α2M) is a 725-kDa plasma glycopro- in man discount sildalis 120 mg with mastercard. Immunological Diseases and Immunopathology 563 Coated pit Clathrin Anti-gp330 IgG gp330 Figure 17 generic sildalis 120 mg online. These immune deposits stain positively for immunizing rats with proximal tubule brush border prepara- IgG and complement by immunofuorescence order sildalis 120 mg mastercard. Affected chil- tions containing subepithelial antigen or Heymann factor, a dren develop fever, nausea, oliguria, and hematuria within 330-kDa protein incorporated in Freund’s adjuvant. The rats 2 weeks following a streptococcal sore throat or skin infec- produce antibodies against brush border antigens, and mem- tion. Erythrocyte casts and mild proteinuria may be identi- branous glomerulonephritis is induced. There may be periorbital edema and hypertension upon bine with shed epithelial cell antigen. Immunoglobulins and idly progressive glomerulonephritis and a few others develop complement are deposited in a granular rather than linear pat- chronic glomerulonephritis. They may also occur in selected other nonstreptococcal postinfectious Heymann’s nephritis: See Heymann glomerulonephritis. Poststreptococcal glomerulonephritis is an acute prolif- IgA nephropathy (Berger’s disease) (Figure 17. It is usually seen in 6- to 10-year-old children, but it may occur in adults as well. A total of 90% of patients have been infected with Group A β hemolytic streptococci that are nephritogenic, specif- cally types 12, 4, and 1 which are revealed by their cell wall M protein. Poststreptococcal glomerulonephritis is mediated by antibodies induced by the streptococcal infection. Immunofuorescence of renal biopsies demonstrates granular immune deposits that Subepithelial deposits contain immunoglobulin and complement in the glomer- uli. The precise streptococcal antigen has never been identifed; however, a cytoplasmic antigen termed endostreptosin together with Humps some cationic streptococcal antigens are found in glomeruli. Patients usually present with gross or Approximately one-third of cases are linked to diabetes microscopic hematuria and often mild proteinuria. There may also be venous onstrating IgA and C3, fxed by the alternative pathway, is thrombosis. Electron microscopy confrms the presence of electron-dense deposits in mesangial areas. Berger’s disease is a type of glomerulonephritis in which C3 is decreased in the serum as a consequence of alternate prominent IgA-containing immune deposits are present complement pathway activation. Patients usually present with gross or increase in sialic acid-rich glomerular basement membrane microscopic hematuria and often mild proteinuria. Patients may possess a serum factor termed microscopy, mesangial widening or proliferation may be nephritic factor that activates the alternate complement path- observed. This factor is an immunoglobulin molecule that reacts onstrating IgA and C3, fxed by the alternative pathway, is with alternate complement pathway-activated components required for diagnosis. Electron microscopy confrms the such as the bimolecular C3b and activated factor B complex. Basement membrane antibody refers to antibodies specifc for the basement membrane of various tissues such as the Dense deposits in glomerul capillary basement membrane Figure 17. This antibody is usually observed by immunofuo- sera of Goodpasture syndrome patients. It is a disease with Linear staining is the interaction of IgG and possibly C3 pulmonary hemorrhage (with coughing up blood) and glom- on peripheral capillary loops of renal glomeruli in antiglom- erulonephritis (with blood in the urine), induced by antiglom- erular basement membrane diseases such as Goodpasture erular basement membrane autoantibodies that also interact syndrome. The use of fuorescein-labeled goat or rabbit anti- with alveolar basement membrane antigens. A linear pattern immunoglobulin preparations permits this smooth, thin, of immunofuorescent staining confrms interaction of the delicate, ribbon-like staining pattern to be recognized by IgG antibodies with basement membrane antigens in the kid- immunofuorescence microscopy. It is in sharp contrast to the ney and lung, leading to membrane injury with pulmonary lumpy bumpy pattern of immunofuorescence staining seen hemorrhage and acute (rapidly progressive or crescentic) pro- in immune complex diseases. In addition to linear IgG, membranes nerVouS SySteM may reveal linear staining for C3 (Figure 17. It is present in human in young adult females and has an incidence of 1 in 2500 indi- viduals in the United States. The spinal fuid protein is seldom increased and nerve conduction studies are usually normal. Oligoclonal response is an immune response character- ized by only a few separate clones of immunocompetent cells responding to yield a small number of immunoglobulin bands in agarose gel electrophoresis. Patients express multiple neurological symptoms that are worse at some times Myelin basic protein (Figure 17. There is inhibition of nerve impulse transmis- ent of the lipoprotein myelin that frst appears during late sion. It is a 19-kDa protein that is increased in mul- gait disturbances, ataxia, and hyperactive tendon refexes. T lymphocytes with the V-β 17 variant of in the nervous system, which facilitates demyelination. Autoimmune mechanisms mediated by T cells, which con- stitute the majority of infltrating lymphocytes, are involved. Infected oligodendrocytes are destroyed by restricted electrophoretic mobility may appear as multiple the immune mechanism, and there also may be “innocent distinct oligoclonal bands in the gamma region (Figure 17. There is infammation, syphilis, progressive multifocal leukoencephalopathy, and demyelination, and glial scarring. Periventricular, frontal, subacute sclerosing panencephalitis, and may appear briefy and temporal areas of the brain are frst involved, followed during the course of Guillian-Barré disease, lupus erythema- by regions of the brain stem, optic tracts, and white matter tosus vasculitis, spinal cord compression, diabetes, or amyo- of the cortex with patchy lesions of the spinal cord. The animals involves T cell receptor interaction with an 18-kDa myelin often develop paralysis. The disease can be passively trans- basic protein molecule, which is an organ-specifc antigen of ferred from a sick animal to a healthy one of the same strain nervous system tissue. The immune reaction induces myelinolysis, wasting, and paraly- Cerebrospinal Fluid Electrophoresis sis. Experimental allergic neuritis is an experimental disease induced by injecting rats with peripheral nerve incorporated into Freund’s complete adjuvant. Acute disseminated encephalomyelitis is brain infam- mation that may be a sequela of certain acute viral infec- tions such as measles in children or following vaccination. Elevated quantities of (gamma region) protein and lymphocytes appear in the cerebrospinal fuid. Histopathologically, lymphocytes, plasma cells, and poly- morphonuclear leukocytes may form perivascular infltrates. The pathological changes are probably attributable to immune = Oligoclonal IgG bands reactivity against the central nervous system constituent myelin basic protein and may represent the human equiva- Figure 17. In the physphorylated form, tau is a major sensorimotor neuropathy involving both arms and legs.
The three main families of leukocyte adhesion mol- lead to the formation of granulocytes purchase generic sildalis online, monocytes cheap 120mg sildalis otc, and ecules include the selectins cheap sildalis 120 mg without a prescription, integrins, and immunoglobulin macrophages. These defciencies prevent granulocytes cells from which all lymphocytes are derived. Pluripotent from migrating to extravascular sites of infammation, lead- hematopoietic stem cells give rise to these progenitors. It consists of at least fve high molecular weight glycopro- teins present on the surface of the majority of human leuko- A myeloblast is a myeloid lineage immature hematopoietic cytes (mol wts: 180, 190, 205, and 220 kDa). The variation between the isoforms is all in the of granulocyte precursors and possesses nongranular baso- extracellular region. The principal types of tyrosine phosphatase that is expressed in various isoforms leukocytes in the peripheral blood of man include polymor- on different types of cells, including the different subtypes phonuclear neutrophils, eosinophils and basophils (granulo- of T cells. Leukopenia is the reduction below normal of the number of white blood cells in the peripheral blood. Leukocyte adhesion molecule-1 is a homing protein found on membranes, which combines with target cell specifc gly- coconjugates. It helps to regulate migration of leukocytes A progenitor cell no longer contains the capacity for self- through lymphocytes binding to high endothelial venules and renewal and is committed to the generation of a specifc cell to regulate neutrophil adherence to endothelium at infam- lineage. A lymphoid progenitor cell is a cell belonging to the lym- Leukocyte adhesion proteins are membrane-associated phoid lineage, such as a bone marrow stem cell, that gives dimeric glycoproteins comprised of a unique α subunit and a rise to all lymphocytes. They form frequently following antigenic or mito- regulation of infammatory responses of both immune and genic challenge of lymphoid cells, which leads to enlargement nonimmune origin. The chromatin is densely packed and Mononuclear cells are leukocytes with single, round nuclei stains dark blue with Romanowsky stains. Small lympho- such as lymphocytes and macrophages, in contrast to poly- cytes contain a thin rim of robin’s egg blue cytoplasm; a few morphonuclear leukocytes. Lymphocytes Lymphoid cell series (1) Cell lineages whose members mor- are divided into two principal groups termed B and T lym- phologically resemble lymphocytes, their progenitors, and phocytes, which can be distinguished phenotypically by their their progeny. These include the lymph nodes, thymus, sion of distinctive surface molecules that have precise roles spleen, and gut-associated lymphoid tissue, among others. In addition, natural killer cells, which are large granular lymphocytes, comprise a small percentage Lymphopenia is a decrease below normal in the number of of the lymphocyte population. Lymphopoiesis is the differentiation of hematopoietic stem Lymphocyte specifcity is the restricted and unique epitopes cells into common lymphoid progenitors and ultimately into a lymphocyte may be able to bind based on its expression of lymphocytes. Lymphoreticular is an adjective describing the system A lymphoid cell is a cell of the lymphoid system. The clas- composed of lymphocytes and monocyte-macrophages, as sic lymphoid cell is the lymphocyte. Molecules, Cells, and Tissues of the Immune Response 103 A long-lived lymphocyte is a small lymphocyte derived principally from the thymus that survives for months to years without dividing. An effector lymphocyte is a lymphocyte activated through either specifc or nonspecifc mechanisms to carry out a cer- tain function in the immune response. They are differentiated descendants of an activated leukocyte that remove a non-self- constituent. Most commonly, the term signifes a T lym- In Wright’s and Giemsa-stained blood smears, the nucleus phocyte capable of mediating cytotoxicity, suppression, or stains dark blue and is encircled by a narrow rim of robin’s helper function. Even though most of the lymphocytes look alike, they differ greatly in origin and function. They A nonadherent cell is a cell that fails to stick to a surface differ in other features as well. A lymphocyte is an example of a non- and B lymphocytes and the E rosette subpopulations look adherent cell, whereas macrophages readily adhere to the the same. However, they have different phenotypic sur- glass surface of a tissue culture fask. This is a com- mon designation for resting T and B lymphocytes that are Paracortex is a T lymphocyte thymus-dependent area recirculating. An activated lymphocyte is a lymphocyte whose cell sur- face receptors have interacted with a specifc antigen or with a mitogen such as phytohemagglutinin, concanavalin A, or staphylococcal protein A. The morphologic appear- ance of activated (or stimulated) lymphocytes is character- istic, and in this form the cells are called immunoblasts. The cells increase in size from 15 to 30 mm in diameter; show increased cytoplasmic basophilia; and develop vacuoles, lysosomes, and ribosomal aggregates. The nucleus contains very little chromatin, which is limited to a thin marginal layer, and the nucleolus becomes conspicuous. An activated B lymphocyte may synthesize antibody molecules, whereas an activated T cell may mediate a cellular immune reaction. By light microscopy, resting lymphocytes appear as a dis- tinct and homogeneous population of round cells, each with figure 2. The small lymphocyte variant, which is the predominant morphologic form, is slightly larger than Lymphocyte traffcking is a process that is critical for an erythrocyte. Larger lymphocytes, ranging between 10 interaction of the lymphocyte surface antigen receptor with and 20 μm in diameter, are diffcult to differentiate from epitopes. They have more cytoplasm and may show azuro- the blood into lymphoid and nonlymphoid organs and back philic granules. Intermediate-size forms between the two again to the blood by way of the lymphatics and venules. By phase contrast microscopy, living lym- Lymphocytes remain in the blood circulation for approxi- phocytes show a feeble motility with ameboid movements mately 30 min on each passage. The mirror handle circulation are exchanged approximately 48 times per day, is called a uropod. In large lymphocytes, mitochondria and about 5 × 1011 lymphocytes leave the blood circulation and lysosomes are better visualized, and some cells show each day. The tent lymphocytes specifc for each antigen, lymphocyte traf- different classes of lymphocytes cannot be distinguished by fcking increases the probability of interaction between the light microscopy. By scanning electron microscopy, B lym- lymphocyte and the epitope for which it is specifc. Several phocytes sometimes show a hairy (rough) surface, but this is adhesion molecules participate in receptor–ligand interac- apparently an artifact. Electron microscopy does not provide tions involved in the entry of lymphocytes into lymphoid additional information except for visualization of the cel- organs through endothelial venules. However, under appropriate stimulation, they are capable of consider- Lymphocyte recirculation is the process of lymphocyte able morphologic changes. Lymphocytotrophic is the property of possessing a special attraction or affnity for lymphocytes. Emperipolesis is the intrusion or penetration of a lympho- A naïve lymphocyte is a mature T or B lymphocyte that has cyte into the cytoplasm of another cell followed by passage never been exposed to antigen and is not derived from anti- through the cell.