Blood vessels within lymph nodes: a comparison between pigs and sheep

In sheep, most blood vessels enter the lymph nodes at a discrete hilus, which is where the capsule overlies medullary tissue. In pigs, vessels within the node arise from an extensive network of arteries on the surface, and most vessels penetrate the capsule where it overlies diffuse tissue--the counterpart of the sheep medulla. In both species the blood vessels divide extensively as they approach and supply the dense lymphoid tissue which contains lymph nodules. The blood vessels within sheep lymph nodules are surrounded by a thick layer of amorphous material. The dense lymphoid tissue has an abundant network of venules which have smooth muscle cells in their walls. These venules are involved in lymphocyte migration and in pigs they are lined by high endothelium which is similar to that in most other species, while in sheep the endothelium is much lower. Fenestrated capillaries occur in both pig and sheep lymph nodes.     

Histology and Ultrastructure of the Lymph Nodes of the Buffalo (Bos bubalus)

Pre‐scapular, femoral and mesenteric lymph nodes from five buffalo calves and five buffalo bulls were studied using light and transmission electron microscopy. The nodes were surrounded with a thin capsule of dense connective tissue and smooth muscles. Subcapsular and trabecular lymphatic sinuses were lined with endothelial cells resting on a basement membrane. The cortex was formed by lymphoid follicles and inter‐follicular lymphocytes. Primary and secondary follicles were observed. The medulla was made up of medullary cords of lymphocytes separated by lymphatic sinuses. These sinuses were lined with a discontinuous epithelium and interestingly crossed by reticular fibres. High endothelial venules were found in the paracortical area. Several lymphocytes were observed infiltrating the wall of these venules. The lymph nodes of the Egyptian water buffalo showed a typical structure compared with the majority of mammals, with no age‐related structural variation.     

Distinctive peripheral lymph node hyperplasia of young cats

Peripheral lymph node enlargement was found in 14 of a series of 132 feline lymph node biopsy specimens. Six of nine cats tested had antibodies for feline leukemia virus (FeLV). Half of the cats were clinically normal while the remainder had fever, lethargy, anorexia, and hepatosplenomegaly. There was severe distortion of lymph nodal architecture with variable loss of discernible follicles and sinuses. Histiocytes, lymphocytes, immunoblasts, and plasma cells were present in expanded paracortical regions which encroached on, and occasionally effaced, lymphoid follicles. Postcapillary venules were numerous and prominent throughout the paracortex. The lymphadenopathy was most commonly transient (86% of cases) with subsequent development of lymphoma in one cat. Lymph nodes from seven kittens with experimental FeLV infection were compared with spontaneously enlarged lymph nodes; four of seven had B and T lymphocyte hyperplasia with normal nodal architecture. Three had partial loss of nodal architecture as a result of expanded paracortical regions populated largely by histiocytes and lymphocytes. Proliferation of postcapillary venules was not prominent in nodes from FeLV-infected cats. The cause of spontaneous lymph node hyperplasia of young cats was not determined. However, the similarity of lesions to those of kittens with experimental FeLV infection and the association with FeLV by serologic tests in six of nine cats suggest that this retrovirus may be involved in the pathogenesis of the lesion.     

Lymphocyte recirculation in cattle: patterns of localization by mammary and mesenteric lymph node lymphocytes

We examined patterns of lymphocyte localization in female dairy cattle following infusion of 51Cr-labeled autologous lymphocytes prepared from surgically excised mammary or ileal mesenteric lymph nodes. Labeled lymphocytes prepared from mammary lymph nodes were recovered in proportionally high numbers from mammary and prescapular lymph nodes, and in low numbers from intestinal mesenteric nodes. This pattern was observed in both heifers and lactating cows. In contrast, labeled lymphocytes prepared from ileal mesenteric lymph nodes of lactating cows were recovered in proportionally high numbers from intestinal mesenteric nodes, and in low numbers from mammary and prescapular nodes. These findings, when compared with previous results in sheep and swine, support the hypothesis that lymphocytes do not migrate efficiently between the gut and mammary gland of ruminants.     

Lymphocytes from one side of the bovine mammary gland migrate to the contra lateral gland and lymph node tissue

The four quarters of bovine mammary glands are completely separated and two quarters on each side (right or left) are connected to ipsi lateral supra mammary lymph nodes. It is not clear whether cells infused into the cistern of the mammary gland are capable of migrating to lymph nodes or the general circulation. To examine cell migration, a prescapular lymph node was removed from each of two lactating and three non-lactating dairy cows, and isolated lymphocytes were stained with Hoechst 33342. Autologous stained cells were infused into the mammary gland and then activated by intramammary infusion of zymosan-stimulated serum (source of C5a). After 17 h, Escherichia coli J5 bacterin was infused into the contra lateral mammary gland to mimic infection. After 43 h cows were euthanized and tissue samples (mammary quarters, right and left supra mammary, mesenteric, ileocecal and prescapular lymph nodes, liver and spleen) were collected for microscopic examination as well as flow cytometric analysis. Hoechst stained cells were detected not only in infused quarters, but also in contra lateral quarters as well as in both supra mammary lymph nodes. This indicates that cells infused into the mammary gland migrate to contra lateral tissues and supra mammary lymph nodes.     

Histological, histochemical and immunohistochemical study of the lymph nodes of the one humped camel (Camelus dromedarius)

Prescapular, femoral, mesenteric, mediastinal and splenic lymph nodes from nine camels of one to 12 years of age were studied. There were no obvious structural differences between these different lymph nodes or between the ages. The lymph nodes were surrounded by a capsule formed of two layers, an outer thicker layer of connective tissue and an inner thinner layer mainly of smooth muscles. Trabeculae extended from the inner layer of the capsule dividing the parenchyma characteristically into incomplete lobules. Subcapsular and trabecular lymphatic sinuses were supported by a reticular fiber network. The parenchyma was uniquely different from that of other species, as it was arranged in the form of lymphoid follicles and interfollicular lymphoid tissue. The lymphoid follicles of CD22 positive lymphocytes were supported by a reticular fiber network. This fine network of α-smooth muscle actin positive cells enclosed the lymphoid follicles. The interfollicular tissue was mainly made up of diffusely distributed CD3 positive lymphocytes. MHC class II: DR was expressed by most lymphocytes of the follicles and interfollicular tissue. Lymphatic sinuses and high endothelial venules were found in the interfollicular zone. The lymphatic sinuses were lined by discontinuous endothelial cells. The wall of the high endothelial venules was infiltrated by several lymphocytes and enclosed in a layer of α-smooth muscle actin positive cells. Acid phosphatase positive cells were evenly distributed in the interfollicular zone. A few cells were localized in the lymph follicles. Alkaline phosphatase was observed in the endothelium of the lymphatic sinuses and in the lymphoid follicles.     

Dynamics of mast cells in lymph node following antigenic stimulation

Dynamics of mast cells in rat cervical lymph nodes were examined using conventional histological techniques after injection of Salmonella paratyphi B-H antigen. There was no significant change in the number of mast cells at sixth hour and on the first day of stimulation compared with the controls. The number of mast cells was increased in all lymph node compartments on the second day of stimulation, which continued in the following 3 days. On the eighth day of stimulation, although the mast cell number decreased in the subcapsular area, it was still high in the paracortical area and medullary sinuses of the lymph nodes. On the second day of stimulation, the mast cell number was apparently increased in the subcapsular area than those of the other compartments. In the following days of stimulation, the highest number of mast cells was seen in the medullary sinuses. The highest paracortical mast cell number was determined on the third day of stimulation and some mast cells were observed near the high endothelial venules (HEVs). The changes of mast cell number among the lymph node compartments after antigenic stimulation support the hypothesis that the migration of mast cells occurred. This migration pattern indicates that mast cells enter the lymph node via afferent lymphatics and migrate to the lymph node compartments following antigenic stimulation.     

Lymphocyte localization in lymph nodes of swine: changes induced by lactation

Localization patterns of lymphocytes taken from mammary, ileal mesenteric, or prefemoral lymph nodes of pubescent or lactating swine were examined. Lymphocyte suspensions were prepared from surgically excised lymph nodes, labeled with 51chromium, and infused back into the donors. Eighteen hours later, pigs were killed, and lymph nodes from six different regions examined for radiolabel. The greatest concentrations of labeled cells were consistently recovered from mesenteric and bronchial lymph nodes, with lesser concentrations recovered from mammary and peripheral nodes. This occurred regardless of origin of the infused cells, and in both pubescent and lactating pigs. Although localization patterns were similar, the total recovery of infused mammary node cells in the six nodes examined was consistently higher in lactating than in pubescent pigs. In contrast, recovery of infused mesenteric node cells was lower in lactating than in pubescent pigs.     

Evidence for conservation of peripheral lymphocyte homing receptors between the bovine, murine and human species.

In rodents and humans, lymphocytes circulate throughout the body and return preferentially to their tissues of origin via a process termed homing. The specificity of homing is controlled by the binding of tissue-specific receptors on lymphocytes to ligands on specialized high-walled endothelial venules (HEV) found in lymphoid tissue. The murine and human peripheral lymphocyte homing receptors (PLHR) have been characterized and shown to be similar to each other. We present evidence for a similar receptor in the bovine. Bovine peripheral blood lymphocytes (PBL) bind to the HEV of murine peripheral lymph node tissue in vitro. The same sugars that have been shown to decrease the binding of murine or human lymphocytes to murine HEV also decrease the binding of bovine PBL to murine HEV. Neuraminidase treatment affects lymphocyte binding in a similar manner in the bovine, murine and human species. Phorbol myristate acetate (PMA) stimulation, which has been shown to reduce the expression of murine and human PLHR, also reduces the binding of bovine PBL to murine HEV. These data suggest conservation of PLHR between these species.     

Visceral leishmaniasis in the German shepherd dog. II. Pathology

Three German shepherd dogs were inoculated with Leishmania chagasi and three with Leishmania donovani and the infection was followed for 82 days. All infected dogs developed splenomegaly and lymphadenomegaly. In lymph nodes there was a reduction in lymphocyte population in paracortical areas, extensive proliferation of macrophages in paracortical areas and medullary cords, follicular hyperplasia, and increased numbers of plasma cells. The spleen had decreased numbers of lymphocytes in periarteriolar lymphoid sheaths, proliferation of macrophages in these regions, follicular hyperplasia, and enlargement of the red pulp with clusters of macrophages and plasma cells. The morphology of the tonsil was similar to the lymph nodes. Clusters of macrophages, often containing Leishmania spp, were present in liver, bone marrow, lung, and the intestines. The morphologic changes in lymph nodes and spleen were suggestive of a suppressed cell-mediated immunity and an active humoral immunity. The German shepherd dog may be a useful laboratory model for the study of immunopathologic changes in visceral leishmaniasis.     

Lymphocyte localization in lymph nodes of pubescent, prepartum, and postpartum sheep

It is generally accepted that lymphocytes associated with the mammary mucosal immune system of non-ruminants may be largely derived from gut-associated lymphoid tissue (GALT). The relationship between the mammary immune system and the GALT of ruminants has not been clearly defined. To address this question, we examined patterns of lymphocyte localization in sheep by 51Cr-labeled lymphocytes following infusion back into donor ewes. We found that lymphocytes taken from mammary lymph nodes of pubescent ewes returned preferentially to mammary nodes, while in prepartum and postpartum ewes, mammary node cells localized equally well in mammary and mesenteric lymph nodes. In contrast, ileal mesenteric lymph node cells from pubescent ewes localized equally well in mammary and mesenteric nodes, but in prepartum and postpartum ewes, localization in mammary nodes was markedly reduced. Comparison of the homing patterns of mammary, mesenteric, and peripheral lymph node cells indicated that mammary node cells behaved similarly to peripheral, rather than mesenteric node cells. This information may be relevant to the extent of communication between the gut and mammary gland in ruminants.     

Effect of infections with swine fever virus on immune functions II. Lymphocyte response to mitogens and enumeration of lymphocyte subpopulations

Peripheral blood and spleen lymphocytes from pigs infected with a low-virulent strain of swine fever virus (SFV) were transiently hyporesponsive to the mitogenic action of PHA, PWM and Con A. The mitogenic reactivity of lymphocytes from lymph nodes from such pigs appeared to be enhanced rather than depressed at that time. In addition, hyperresponsiveness of peripheral blood lymphocytes (PBL) to these mitogens occurred in some pigs.PBL from pigs lethally infected with virulent SFV showed a persistent depression of the response to these mitogens, whereas lymphocytes from lymph nodes had a high responding capacity.A lymphocyte response to SFV antigens could not be demonstrated in infected pigs.These SFV infections did not markedly affect the percentage of lymphocytes in the blood and most lymphoid organs rosetting with sheep red blood cells. On the other hand, surface immunoglobulin-bearing lymphocytes were markedly increased in lymph nodes from pigs exposed to virulent SFV. The sum of both lymphocyte subpopulations in the lymph nodes from these pigs often considerably exceeded the 100% value, which strongly suggests the presence of cells bearing both surface immunoglobulin and receptors for dextran-treated sheep red blood cells.Possible correlations between these findings are discussed. The results suggest that infections with SFV induce systemic alterations in the process of lymphocyte recirculation in the pig.     

Lymphocyte subpopulations in spontaneous disease of rhesus macaques.

The immunologic status of rhesus macaques (Macaca mulatta) with naturally occurring disease was evaluated by determining the percentages of B and T lymphocytes and mitogen responsiveness of lymphocytes in peripheral blood and lymph nodes. The B lymphocytes were identified by the presence of cell surface immunoglobulin and receptors for complement. The T lymphocytes were identified by their ability to form spontaneous rosettes with sheep red blood cells. Rhesus macaques with idiopathic or primary amyloidosis had normal lymphocyte characteristics. Peripheral blood lymphocytes from rhesus macaques with atypical tuberculosis had decreased percentages of spontaneous rosette-forming cells and depressed responses to concanavalin A, and those with chronic diarrhea or chronic arthritis were also found to have abnormal peripheral blood lymphocyte characteristics. The percentage of B and T lymphocytes in normal lymph nodes was variable, making simultaneous histologic examination necessary for evaluation of diseased animals.     

Intestinal uptake of intact maternal lymphocytes by neonatal rats and lambs

Two experiments were conducted using neonatal rats and lambs. The intestinal lumen of neonatal rats was infused with radiolabelled syngeneic lymphocytes, whereas the intestine of lambs was infused with radiolabelled allogeneic maternal lymphocytes. The results of both experiments indicated that radiolabelled cells were absorbed by the intestine as judged by autoradiographic studies of intestinal tissue. Furthermore, in lambs it was possible to show that these cells were transported via the lacteal lymph ducts to the mesenteric lymph nodes. These findings suggest another mechanism by which the lactating ewe may confer immunity to its suckled young.     

Local immunity in the mammary gland.

The mammary glands of pregnant and non-pregnant sheep were stimulated by infusion of killed Staphylococcus aureus, and the lymphoid cell response delineated with a panel of monoclonal antibodies. Seven days after antigen infusion, the mammary glands of both pregnant and non-pregnant sheep displayed a striking feature, characterised by the presence of numerous CD45R+ MHC class II+ B cells in the periductal connective tissues. These cells were seen to be clustering around blood capillaries with very prominent endothelial cell lining. Some CD5+ CD4+ lymphocytes were scattered among the B-cell clusters, whereas a few CD8+ lymphocytes were seen mainly at the periphery of the B-cell clusters. Fourteen days after antigen infusion, numerous plasma cells were observed, most of them being of the IgA isotype. Seven days after parturition (approximately 40 days after antigen infusion) the number of lymphocytes and plasma cells in the infused glands had declined dramatically. These data indicate that B cell and helper T-cell interaction can take place at the local sites of antigen stimulation in the mammary gland.     

Response of efferent lymph and popliteal lymph node to epidermal infection of sheep with orf virus

Functional and phenotypic changes in the cell populations were monitored in the popliteal efferent lymph of sheep following experimental epidermal infection with orf virus. In another group of sheep, cells from the popliteal lymph node draining the site of infection were similarly monitored and compared with the cells from contralateral popliteal and mesenteric lymph nodes. All sheep showed serological evidence of previous exposure to orf virus. Following infection, anti-orf antibody titres rose and efferent lymphocyte and blast cell output increased. Interferon-like activity was detected in efferent lymph early after orf virus but not mock infection. Lymphocytes from the draining popliteal lymph node showed antigen-specific lymphoproliferation on Days 3-7 while cells in the efferent lymph demonstrated proliferative activity on Days 4-6. The requirement for exogenous antigen-presenting cells in the culture of efferent lymphocytes varied between individual sheep. The culture supernatant from proliferating lymph node cells contained interferon-like activity but no anti-orf antibodies, the reverse of that from cultured efferent lymphocytes, perhaps indicating a different reactive T cell population. During the course of the experiment there was an increase in the percentage of efferent lymphocytes expressing MHC Class II antigens and surface immunoglobulins, the latter being recorded as a double peak. The short-term nature of the local T cell response may in part explain the incompleteness of immunity to orf virus in sheep.     

Evidence of decreased concanavalin A induced suppressor cell activity in the peripheral blood and pulmonary lymph nodes of sheep with ovine progressive pneumonia

Concanavalin A (Con A) induced suppressor cell activity was evaluated in a group of ovine progressive pneumonia virus-antibody positive sheep (OPPV+). Decreased levels of suppressor activity were observed in the peripheral blood and regional pulmonary lymph nodes of animals with clinical and pathological evidence of ovine progressive pneumonia (OPP) when compared to animals with no lesions and animals with caseous lymphadenitis involving the lungs and pulmonary lymph nodes. Decreased levels of Con A stimulated lymphocyte proliferation was also observed in the peripheral blood and iliac lymph nodes of sheep with OPP. Sheep with OPP were found to be hypogammaglobulinemic. Sera from OPPV+ sheep had no effect on T and B cell mitogen stimulated responses of lymphocytes from sheep seronegative for antibodies to ovine progressive pneumonia virus (OPPV-) when compared to normal sheep serum.     

Observations on blood leucocytes and lymphocyte subsets in sheep infected with bovine leukaemia virus: a progressive study

Haematological parameters and reactivity of lymphocyte antigens to monoclonal antibodies were studied over a 10-month period in sheep experimentally infected with bovine leukaemia virus (BLV). BLV-inoculated animals seroconverted within 1 month and showed a significant lymphocytosis 2-6 weeks after infection. Control animals inoculated with BLV-free lymphocytes showed a stronger and more immediate neutrophil response than those inoculated with BLV-positive lymphocytes. One month after infection, BLV-inoculated sheep showed a relative increase of cells bearing antigens T4, T6, T8 and T19, and 10 months into the trial, MHC II lymphocytes increased, T6 remained elevated, but T4 helper cells were significantly decreased in number. Lymphoma tissue showed the presence of T8 cells, and lymph nodes from seroconverted sheep had areas of concentrated T4 staining cells. These results demonstrate responses in cellular immune mechanisms to infection with BLV.     

Immunomorphologic and morphometric changes in pulmonary lymph nodes of sheep with progressive pneumonia

Morphologic, immunohistochemical, and morphometric studies were conducted on the posterior mediastinal lymph nodes of eleven sheep with naturally occurring ovine progressive pneumonia and four apparently healthy sheep with no pulmonary lesions (three seropositive, one seronegative for antibody to ovine progressive pneumonia virus). Compared with lesion-free sheep, sheep with ovine progressive pneumonia had a seven-fold increase in B lymphocyte areas and a 21/2-fold increase in T lymphocyte areas of these lymph nodes. Immunochemistry revealed cytoplasmic immunoglobulin G in scattered cells of germinal centers, medullary cords and interfollicular areas and membrane-associated immunoglobulin G in dendritic cells of germinal centers. Immunoglobulin M staining cells were widely scattered in germinal centers and medullary cords. Although B cell hyperplasia seemed to be the predominant process in lymph nodes of sheep with ovine progressive pneumonia, this was not accompanied by the expected degree of plasmacytosis, morphologically and immunohistochemically. These findings may represent an aberrancy of immunoregulation in ovine progressive pneumonia.