Bone marrow transplantation in the rat. Lytic functions of inflammatory leukocytes during acute graft-versus-host disease

We have isolated inflammatory leukocytes from various lymphoid and parenchymal organs after total body irradiation and bone marrow transplantation from either an allogeneic or syngeneic strain and tested their ability to perform lytic functions in vitro. No direct lytic activity (i.e. cytotoxic T lymphocytes, CTL) to relevant strain-derived target cells in the lymphoid or parenchymal target organs was seen preceding or during acute graft-versus-host disease (aGVHD). Instead, the leukocytes of the spleen and blood and the inflammatory cells of liver and lungs were efficient effector cells against recipient-derived target cells in the presence of relevant antibody (antibody dependent cellular cytotoxicity, ADCC). The NK activity against YAC-1 (natural killer, NK) target cells was first high in the spleen, but when the aGHVD appeared in the allograft marrow recipients the NK activity decreased in the spleen with a concomitant increase in the liver, but not in the other parenchymal target organs. At the same time no NK activity was seen in the syngeneic marrow graft recipients' parenchymal organs. These observations suggest functional differences in the structure of inflammation in the different target organs of aGVHD.     

Early events in liver allograft rejection. Delineation of sites of simultaneous intragraft and recipient lymphoid tissue sensitization.

The early events of liver allograft rejection in untreated rats were studied in the DA to BN rejection strain combination and compared with DA and BN liver isograft recipients. In the liver allografts, T-cell infiltration first occurred at 2 days after transplantation and localized to the portal triads and subjacent to the terminal hepatic venules (THV), regions rich in intensely Ia + spindle and dendritic-shaped interstitial cells. Double staining showed distinct 'clustering' between donor Ia-positive dendritic-shaped cells and W3/25+ infiltrating lymphocytes, or to a lesser extent, OX8+ cells. The infiltrating mononuclear cells underwent blastogenesis and proliferated in both the triads and THV regions at 3 and 4 days. Donor Ia-positive cells were also noted in the W3/25+ periarterial lymphatic sheath and marginal zone of the recipient spleen 1 day after transplantation. The number of these cells in the spleen peaked at 3 to 4 days, but were no longer detectable by 10 to 12 days. Mitotic activity became evident in these same regions by days 3 and 4. Paracortical blastogenesis (day 2) and proliferation (days 3 and 4) were also noted in the regional lymph nodes of liver allograft recipients, but no donor Ia+ cells were found in the mesenteric nodes or thymus of the allograft recipients. These results demonstrate that sensitization of the recipient lymphoid tissue to liver allografts can occur both peripherally (intragraft) and centrally (spleen and lymph nodes). Passenger leukocytes (donor dendritic cells) are likely the primary stimulators of the rejection reaction. Still, it is probable that other pathways of sensitization exist.     

Thyroiditis in T cell-depleted rats: suppression of the autoallergic response by reconstitution with normal lymphoid cells.

Qualititive, quantitative and functional differences were found in lymphoid cells of female thymectomized and irradiated (Tx-X) PVG/c strain rats as compared to normal females of the same strain. Tx-X rats were lymphopenic and had reduced numbers of cells within spleen and cervical lymph nodes, depressed transformation responses of peripheral blood lymphocytes to PHA and lower percentage killing of their spleen cells by anti-T-cell serum and complement. There was an increased percentage of immunoglobulin-bearing cells in the lymph nodes. Reconstitution of Tx-X rats by the intravenous route using syngeneic lymph node cells, spleen cells or thymocytes abrogated the autoimmune responses to thyroid components generally observed in this state. Lymph node and spleen cells, but not thymocytes, also prevented thyroid changes when given intraperitoneally. In contrast, bone marrow cells appeared to give enhanced responses. Quntitative studies showed that the relative proportions of the suppressor or autoregulatory cells in various lymphoid tissues were lymph node greater than spleen greater than thymus. Complete abrogation of the autoimmune responses was possible only when cells were administered within a short time of final dose of irradiation and moderate thyroid change was again seen if transfer was delayed for 14 days post-irradiation. At 28 days reconstitution had no influence on the development of the autoimmune responses. Preliminary characterization studies using an anti-T-cell serum and fractionation of lymph node cells on a linear Ficoll gradient suggested that autoregulatory cell is a large T cell.     

Immunohistology of skin and rectum biopsies in bone marrow transplant recipients.

We have studied histological and immunohistological specimens of 39 skin biopsies from 21, and 30 rectal biopsies from 17 bone marrow transplant recipients. The biopsies were taken before transplantation, during acute and chronic graft-versus-host disease (GVHD), and at times with no GVHD. In biopsies taken during cutaneous aGVHD grade I to III, epithelial changes were seen in 16/23 biopsies. The cutaneous infiltrates during aGVHD consisted of CD2-, CD4-, CD8- and FMC-33-positive cells both in the epithelium and in the dermis. CD57-positive NK cells were also detected in most biopsies. During chronic GVHD the cutaneous cellular infiltrates were similar to those seen in moderate aGVHD, i.e. both CD4- and CD8-positive lymphoid cells were present. When the biopsy was taken after the beginning of corticosteroid treatment for aGVHD, or at times when the patient did not have GVHD symptoms, the cellular infiltrates were considerably smaller in the dermis. During clinical intestinal aGVHD mucosal epithelial changes were relatively uncommon; instead, increased numbers of both CD4- and CD8-positive lymphocytes in the lamina propria (LP) were seen in 11/13 samples. During chronic GVHD the number of CD4-positive cells exceeded that of CD8-positive cells in the LP, and the large lymphoid infiltrates also reached the muscularis mucosae. In rectal biopsies the differences were not so prominent because most of the pretransplant biopsies showed CD2-, CD4-, CD8- and CD57-positive lymphocytes both in the lamina propria and epithelium.     

The development of lymphocytes with T- or B-membrane determinants in the human foetus

The development of T- or B-membrane determinants on human foetal lymphoid cells was studied by the direct immunofluorescence technique, using a tetramethyl rhodamine isothiocyanate (TRITC) labelled horse antihuman T-cell conjugate (ATC) for the detection of T lymphocytes and a fluorescein isothiocyanate (FITC) labelled goat antihuman Fab conjugate for the demonstration of Ig-bearing B lymphocytes. Human foetal lymphocytes were also tested for spontaneous rosette formation with sheep red blood cells (SRBC).

Cell suspensions of liver, spleen, thymus, bone marrow and blood of twenty-five human foetuses of 5·5–26 weeks of gestational age have been investigated. ATC-positive lymphoid cells were first seen in the liver at 5·5 weeks; E rosette-forming cells (ERFC) and Ig-bearing lymphoid cells were first found at 9 weeks. ERFC were also present in the thymus at 9 weeks. By 12 weeks, fluorescent B and T lymphocytes were found in bone marrow and spleen. ERFC were also found in bone marrow at this age, but not in spleen. At 15 weeks, more than 80% of blood lymphoid cells had T or B determinants.

A difference in the reactivity of lymphoid cells with the ATC and their capacity to form E rosettes was observed. In liver and spleen, the ATC determinant was detectable before the SRBC receptor. In bone marrow, blood and thymus the ATC determinant was found on a higher percentage of lymphoid cells than was the SRBC receptor when those organs were first investigated. During the entire investigated period of gestation, the majority of lymphoid cells in liver and bone marrow did not react with either of the conjugates, nor did they form E rosettes. In all organs investigated, except in the thymus, lymphoid cells were occasionally seen which reacted with both conjugates. By the 16th week of foetal age, more than 90% of lymphoid cells in thymus, spleen and blood had acquired T- or B-membrane determinants.

     

Cell transplantation into immunodeficient chicken embryos. Reconstituting capacity of cells from the yolk sac at different stages of development and from the liver, thymus, bursa of Fabricius, spleen and bone marrow of 15-day embryos.

Cyclophosphamide-treated 18-day-old chicken embryos were transplanted with histocompatible cells from the yolk sac at different stages of development and from the liver, thymus, bursa of Fabricius, spleen and bone marrow of 15-day-old-embryos. At the age of 36 days, the cell recipients were studied to determine the reconstitution capacity of the transplanted cells. The parameters used include the survival pattern, gain of body weight, antibody-forming capacity, response of peripheral blood lymphocytes to Con A, weight and microscopic morphology of the bursa of Fabricius, and weight of spleen and thymus. By all the criteria employed, only bursa cells were capable of a functional and morphological reconstitution of the recipient's humoral immune system. These data indicate that the role of the yolk sac as the first generator of prebursal stem cells remains questionable. In addition, these findings confirm the previous observations that, as a differentiation site of the B-cell lineage, the bursa of Fabricius precedes the bone marrow during ontogenetic development.     

Blastogenic response of lymphocytes separated from bone marrow to allogeneic lymphoid cells in vitro

Fractions of cells were separated from the bone marrow and spleen of Lewis rats by brief centrifugation in linear sucrose-serum density gradients and were cultured in vitro either alone or mixed with F₁ (Lewis × Brown Norway) hybrid rat lymphoid cells. After 4 days the incorporation of [³H]thymidine into DNA was measured by scintillation counting, and the morphology and incidence of [³H]thymidine-labelled cells were determined in radioautographs.

Lymphocyte-rich, slowly-sedimenting fractions of Lewis rat bone marrow cells showed increased incorporation of [³H]thymidine and the development of many large proliferating blast-like cells when cultured with F₁ hybrid cells. This blastogenic response was greater than could be ascribed to contaminating intravascular blood lymphocytes. Slowly-sedimenting fractions of spleen cells, consisting mainly of small lymphocytes, showed a greater blastogenic responsiveness to F₁ hybrid cells than that of whole spleen, while rapidly-sedimenting spleen cell fractions, containing many large cells, showed a reduced responsiveness. Paradoxically, rapidly-sedimenting marrow cell fractions containing few small lymphocytes, showed an increment in [³H]thymidine incorporation when cultured with F₁ cells but this was due to active macrophage proliferation as well as to blastogenesis.

The results demonstrate that some parenchymal bone marrow lymphocytes undergo blastogenic transformation in response to allogeneic lymphocytes in vitro.

     

The different migratory characteristics of lymphocyte populations from a whole spleen transplant.

Spleens from AS x BN donor rats labelled in vivo by multiple doses of [3H]thymidine were transplanted into syngeneic recipients by anastomosis to the abdominal great vessels. The recipients were killed 1-5 days after receiving the whole spleen transplants and the numbers and location of the [3H]thymidine-labelled cells which had migrated from the labelled donor spleen traced by means of autoradiographs of sections, imprints and smears of various recipient lymphoid tissues. These results were compared with the migration pattern of labelled dissociated spleen cell suspensions injected intravenously. The latter consists almost entirely of small lymphocytes which migrate to T or B areas of recipient spleen, lymph nodes and Peyer's patches. The labelled whole spleens also contained cells which migrated to the T and B areas of recipient lymphoid tissues, but in addition contained many lymphoid cells which migrated to the red pulp of the recipient spleen and to the lamina propria of the gut. These experiments showed, therefore, that the spleen contains mobile elements which have not been detected by transfer of spleen cell suspensions.     

Effects of fowl adenovirus infection on the immune system of chickens.

A virulent strain of serotype 8 fowl adenovirus (FAV) was isolated from an outbreak of inclusion body hepatitis (IBH) in broiler flocks. Post-mortem changes included characteristic liver lesions with intranuclear inclusion bodies in the hepatocytes and severe lymphocytic depletion in the bursa, thymus and spleen. The packed cell volume was reduced by 50 per cent or more and varying amounts of cell depletion were observed in the bone marrow. Typical IBH was reproduced in specific pathogen-free chickens inoculated orally with the FAV isolated from the natural infection. There was severe depletion of lymphocytes in the bursa, thymus and spleen of the experimentally infected birds and FAV antigens were detected by ELISA and immunocytochemical staining in various lymphoid tissues. Humoral antibody responses against sheep red blood cells, detected by the haemagglutination test, were decreased in the chickens infected with FAV. These findings suggest that the damage caused by replication of this virulent strain of FAV in lymphoid tissues compromises the immunological capabilities of infected chickens.     

Bone Marrow Transplantation in the Rat

We have analysed the cytological structure of inflammation in the different parenchymal target organs during acute graft-versus-host disease after bone marrow transplantation in the rat. Inflammation (recovery of increased numbers of white cells) was recorded in the liver, skin, and lungs of the allograft recipient compared with the syngeneic graft recipient from day 5 onwards, accompanied by reduced recovery of inflammatory cells from the gut. The major cytological manifestation of the disorder was an increase in the total number of blast cells, large granular lymphocytes (LGL), and lymphocytes in the liver and skin, and of the number of blast cells and LGL in the lung. At the same time, a depletion of LGL and lymphocytes was recorded in the blood, suggesting migration of these cell components to the site of inflammation.     

Bone marrow transplantation in the rat. III. Structure of the liver inflammatory lesion in acute graft-versus-host disease.

The liver is a major parenchymal target organ of acute graft-versus-host disease (aGVHD) after bone marrow transplantation in the rat. The authors have analyzed the nature of cellular infiltrates in the liver using monoclonal antibodies against white cell subsets and investigated the anatomic distribution of the inflammatory cell subsets inside the liver parenchyma. Several types of white cells are present in a normal control liver: In the portal area the T-helper (Th) cells predominate, (surface) immunoglobulin-expressing B cells are present in ample numbers, and most of the phagocytes are Ia-positive. In the central vein area the T-suppressor/killer cells (Tsk) dominate, no B cells are present, and most of the phagocytes are Ia-negative. During aGVHD the number of T cells increases rapidly in the portal area; and after an initial strong increase, the Th/Tsk ratio decreases but remains still above 1. In the central vein area there is also an increase in the number of T cells, compared with that in the syngeneic recipient, but the Th/Tsk ratio rapidly decreases and remains uniformly below 1. During aGVHD the B cells entirely disappear from the portal area, whereas a small but distinct number of mature plasma cells with intracellular immunoglobulin appear in the central vein area. Following irradiation the Ia-positive phagocytic cells entirely disappear from the portal area and decrease distinctly in number in the central vein area. During aGVHD the number of Ia-positive phagocytes increases again in both locations. In the central vein area the positive phagocytes are seen over the background level, and, concomitantly, the Ia-negative phagocytes disappear.     

Cytology and histology of haemopoietic cell transplantation under the influence of ALS in mice. II. The effect of marrow from donors pretreated with antilymphocyte serum (ALS) on the recipient

Cytology and histology of recipients of allogeneic bone marrow were studied 13. 20, 24, 30 and 34 days after transplantation. The developing chronic secondary disease was characterized by increased numbers of myeloid cells, by lymphopenia and by erythroblastopenia in the bone marrow and the spleen. Erythroblastopenia together with lymphopenia and augmented myeloid cells also occurred in irradiated F₁-hybrids suffering from a chronic homologous disease. The latter model eliminated the following as a cause of erythroblastopenia in secondary disease: (1) host-versus-graft reaction against donor-type erythroblasts for immunogenetical reasons, and (2) graft-versus-host reaction against recipient-type erythroblasts since they had already been destroyed by irradiation. Treatment of the donor with ALS resulted in a suppression of homologous disease in F₁-hybrids with a cytology resembling that of recipients of syngeneic spleen cells. The same treatment only delayed the onset of chronic secondary disease in recipients of allogeneic bone marrow. These allogeneic recipients, in contrast to the F₁-hybrid recipients, died with the typical morphology of a chronic secondary disease.

In recipients of syngeneic bone marrow from donors treated with ALS, repopulation with lymphocytes was somewhat delayed and transient erythroblastosis in the spleen occurred 20 days after transplantation.

     

CD8 T-cell recognition of macrophages and hepatocytes results in immunity to Listeria monocytogenes.

CD8 T cells are effective mediators of specific immunity to infection by Listeria monocytogenes, a bacterial pathogen that initially infects macrophages in the spleen and liver and subsequently spreads to hepatocytes and unidentified parenchymal cells in the spleen. To identify the in vivo target cells of L. monocytogenes-immune CD8 T cells, adoptive transfer assays were performed with bone marrow chimeric or transgenic host mice which had been manipulated to alter the major histocompatibility complex molecules expressed on macrophages or hepatocytes. L. monocytogenes-immune CD8 T cells mediate significant immunity in BDF1-->beta 2 M-/- chimeras, comparable to that seen in unmanipulated BDF1 recipients. L. monocytogenes-immune CD8 T cells also mediate significant antilisterial immunity in parent-->F1 chimeras when the CD8 T cells are syngeneic with the bone marrow donor. These data demonstrate that bone marrow-derived macrophages are major targets for L. monocytogenes-immune CD8 T cells in adoptive transfer assays. Interestingly, significant immunity was observed in parent-->F1 chimeras when the L. monocytogenes-immune CD8 T cells were not syngeneic with the bone marrow donor, suggesting that recognition of Listeria-infected non-bone-marrow-derived cells such as hepatocytes may also occur in vivo. Consistent with this possibility, H-2Kb-restricted CD8 T cells specific for the listeriolysin O molecule mediate significant immunity in the liver, but not the spleen, in transgenic mice expressing H-2Kb only on hepatocytes. In addition, Listeria-specific CD8 T cells lyse Listeria-infected hepatocyte-like cells in vitro. Thus, Listeria-infected hepatocytes can be recognized by CD8 T cells in vivo and in vitro.     

Immunological capacity of the chicken embryo. I. Relationship between the maturation of lymphoid tissues and the occurrence of cell-mediated immunity in the developing chicken embryo.

In an investigation of the ontogeny of lymphoid tissue in chick embryos to relate maturation of lymphocytes with immunological competence, the numbers and sizes of lymphocytes were determined in the thymus, bursa of Fabricius, spleen, femoral marrow and peripheral blood of embryos from the 12th to 21st day of incubation, and in 6-day-old chicks. Results showed the thymus to be the first fully developed and most active lymphocytopoietic organ, followed by the bursa. The bone marrow was not lymphocytopoietic; the spleen and bone marrow were mainly granulocytopoietic and erythropoietic; some morphological differences between thymic and bursal lymphocytes were shown by light microscopy. It appears that in embryos and young chicks the lymphocytes are derived from the thymus and bursa, but not the bone marrow. In tests of immunological competency, cells of the thymus, bursa, spleen, bone marrow and peripheral blood from 12--21-day-old embryos and 6-day-old chicks were transferred to chorioallantoic membranes of 12-day-old recipient embryos. There were distinct differences between the ability of various lymphoid tissues to induce formation of chorioallantoic pocks or splenic enlargement. The thymus, spleen and peripheral blood elicited both lymphocytic pocks and splenomegaly, the bursa elicited splenomegaly only, and the bone marrow was ineffective. The bone marrow, however, induced formation of nonlymphocytic pocks. It is concluded that the immunological activity of the chicken embryo is primarily effected by the thymus and bursa and that cell-mediated immunity appears in the 2nd week of incubation.     

Induction of acute graft vs. host disease in lymphopenic mice

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially life-saving treatment for refractory/relapsing hematological malignancies, blood disorders or autoimmune diseases. However, approximately 40–50% of patients undergoing allogeneic HSCT will develop a multi-organ, inflammatory disorder called acute graft vs. host disease (aGVHD). Experimental and clinical studies suggest that intestinal injury due to toxic, pre-transplant conditioning protocols (e.g. lethal irradiation and/or chemotherapy) may play a major role in the development of aGVHD. However, recent studies from our laboratory suggest that this may not be the case. The objective of this study was to quantify and compare the onset and severity of aGVHD induced by the adoptive transfer of allogeneic T cells into untreated lymphopenic mice. Four million allogeneic or syngeneic CD4⁺CD62L⁺CD25⁻ T cells were transferred (i.p.) into NK cell-depleted RAG1^-/- mice or RAG2^-/-IL2rγ^-/- double knock-out (DKO) mice and assessed daily for signs of aGVHD. We found that adoptive transfer of allogeneic but not syngeneic T cells into NK cell-depleted RAG1^-/- or DKO mice induced many of the clinical and histological features of aGVHD including weight loss, inflammatory cytokine production and tissue inflammation. In addition, adoptive transfer of allogeneic T cells into each recipient induced severe anemia as well as dramatic reductions in bone marrow and spleen cellularity. Taken together, we conclude that allogeneic CD4⁺ T cells are both necessary and sufficient to induce aGVHD in lymphopenic recipients in the absence of toxic, pre-transplant conditioning.     

Cells involved in the immune response: XXVI. The demonstration of bone-marrow specific antigens in the rabbit

Horse anti-rabbit bone marrow cell antiserum was tested for its cytotoxic activity with respect to the lymphocytes of the various lymphoid organs. The unabsorbed antiserum was highly cytotoxic with respect to the circulating WBC and cells of the bone marrow and thymus but demonstrated low cytotoxic activity with respect to spleen, lymph node and SAPP cells (sacculus rotundus, appendix and Peyer's patches). However, following absorption with thymocytes, lymph node cells or SAPP cells, cytotoxic activity directed toward any of these cell types disappeared without affecting the cytotoxic activity with respect to bone marrow and circulating lymphocytes. On the other hand, bone marrow and spleen cells and circulating white blood cells were capable of absorbing out completely the cytotoxic activity directed toward these cells. On the basis of a comparison of efficiency of absorption of anti-bone marrow cell activity by cells of the different lymphoid organs and cytotoxicity assays of the absorbed antiserum, it is concluded that approximately 15–25 per cent of the spleen lymphocytes and 20–40 per cent of the circulating lymphocytes in the rabbit are bone marrow-derived cells. The other lymphoid organs do not normally appear to possess these cells.     

Marrow ablative doses of gamma-irradiation and protracted changes in peripheral lymph node microvasculature of murine and human bone marrow transplant recipients

Gamma-irradiation has been extensively utilized as a bone marrow ablative agent during human bone marrow transplantation. Although the effects of ionizing radiation on lymphoid and hematopoietic cells are well documented, little is currently known about its effect on the nonhematopoietic tissues which are important for the restoration of normal immune function. The vast majority of lymphocyte movement into peripheral lymph nodes takes place via the bloodstream and requires a specific receptor-ligand interaction between the lymphocyte and anatomically distinct postcapillary venules. Due to the importance of lymphocyte recirculation in the initiation and amplification of immune responses, an understanding of the radiosensitivity of the postcapillary venules may provide insight into the pathogenesis of the immune deficiencies commonly seen after bone marrow transplantation. Our studies disclosed that the ability of normal blood-borne lymphocytes to enter peripheral lymph nodes was markedly depressed (less than 50% of normal) in mice which had been exposed to 7.5 Gy of gamma-irradiation. This radiation-induced effect lasted longer than 6 months after irradiation and syngeneic reconstitution, and its magnitude was radiation-dose dependent. Immunochemical staining of the lymph node microvasculature with the monoclonal antibody MECA-325 established that the radiation protocol induced persistent anatomic changes in the lymphocyte-receptive areas of endothelium (high endothelial venules). These vessels developed the appearance of endothelial cell proliferation. Electron microscopy demonstrated significant intracellular edema, with virtual occlusion of many microvascular lumens by edematous endothelial cells. Lymph nodes from human bone marrow transplant recipients were found to exhibit similar ultrastructural changes. These studies for the first time demonstrate that doses of irradiation similar to those used to prepare bone marrow transplant recipients can have significant anatomic and functional sequellae on host endothelial cells.     

Lymphocyte-mediated cytotoxicity against tumor cells. III Differentiation of concanavalin A-activated cytotoxic effector cells.

The maturation of selected T cell responses in the lymphoid organs of irradiated CBA mice was followed after adoptive transfer of syngeneic fetal liver cells. Mitogenic responsiveness to phytohemagglutinin (PHA) and concanavalin A (Con A) was found to reach control values 3 weeks after reconstitution in the thymus, spleen, and lymph node, of fetal liver repopulated animals. Spleen and lymph node cell reactivity in mixed lymphocyte culture reactions required 6 weeks to reach significant values. However, the ability of spleen cell suspensions to be activated by Con A into cytotoxic effector lymphocytes appeared after only 2 to 3 weeks. It is concluded that two functionally distinct T cell subpopulations exist in the spleen, one which can be activated into cytotoxic effector lymphocytes by Con A, and one which responds to alloantigens by DNA synthesis.     

Splenectomy increases mortality in murine Trypanosoma cruzi infection

The spleen is a secondary lymphoid organ that harbours a variety of cells such as T and B lymphocytes and antigen‐presenting cells important to immune response development. In this study, we evaluated the impact of spleen removal in the immune response to experimental Trypanosoma cruzi infection. C57BL/6 mice were infected with Y strain of the parasite and infection was followed daily. Mice that underwent splenectomy had fewer parasites in peripheral blood at the peak of infection; however, mortality was increased. Histological analysis of heart and liver tissues revealed an increased number of parasites and inflammatory infiltrates at these sites. Spleen removal was associated with reduction in IFN‐γ and TNF‐α production during infection as well as with a decrease in specific antibody secretion. Haematological disorders were also detected. Splenectomized mice exhibited severe anaemia and decreased bone marrow cell numbers. Our results indicate that spleen integrity is critical in T. cruzi infection for the immune response against the parasite, as well as for the control of bone marrow haematological function.     

Cytomegalovirus-induced mononucleosis in guinea pigs.

The effects of cytomegalovirus (CMV) infection on hematopoietic and lymphoid tissues were studied in guinea pigs. Blood parameters, histopathology, and virus distribution in the bone marrow, spleen, lymph nodes, and thymus were assessed during primary nonlethal acute and chronic guinea pig CMV infection. Transient hematological changes comparable to those seen in human CMV mononucleosis were observed during acute infection. These included anemia and leukocytosis with atypical lymphocytes. Splenomegaly and stimulation of spleen and lymph node T- and B-cell areas were also noted. These changes occurred at the peak of virus recovery from all tissues tested, as well as from macrophages and B- and T- cell-enriched spleen subpopulations. Virus was cleared rapidly from blood and bone marrow; blood counts, spleen size, and histology returned to normal within 1 month after virus inoculation. However, guinea pigs failed to eliminate the virus completely from lymphoid tissues, since virus persisted in splenic macrophage and B-lymphocyte-enriched populations during chronic infection. The data suggest that CMV-infected mononuclear cells play a role in the establishment of generalized acute infection and virus persistence.