Ontogeny and organization of the stationary non-lymphoid cells in the human thymus

Summary Ontogenetic differentiation of the human thymus was investigated in 50 embryos by means of light and electron microscopic methods in an attempt to clarify the morphogenesis of the complicated microecology of thymic tissue. At the 8th gestational week (g.w.), the primordium of the thymus contains almost exclusively undifferentiated epithelial cells. At the 10th g.w., the epithelial cells in the central part are spindle-shaped. During the subsequent weeks the cortical region of the thymus becomes separated into lobes by mesenchymal septa containing hemopoietic precursor cells and large electronlucent cells with irregularly shaped nuclei. The latter cells are also found in the deeper presumptive medullary regions of the thymus; they differentiate into interdigitating reticulum cells (IDC). The permeation of the medulla of the thymus by non-epithelial IDC occurs concurrently with the formation of cortical and medullary epithelial cells. Between the 12th and 14th g.w. the cortical and medullary differentiation is completed. At this time-stage cortical small lymphocytes differ in morphological shape from medullary lymphocytes, the latter acquiring the appearance of immunocompetent T cells and establishing intimate contact with the IDC.These findings indicate that the thymic cortex and medulla contain different epithelial cells. In addition, the thymic medulla displays cells characterized by the morphology of typical interdigitating reticulum cells of peripheral lymphoid tissue. The structural pattern of the thymus is correlated to morphologically differing lymphoid cell populations in the cortical and medullary regions.This investigation was supported by grants from the Deutsche Forschungsgemeinschaft and by the Sonderforschungsbereich 111The authors dedicate this paper to Professor Helmut Leonhardt on the occasion of his 60th birthday. The authors also appreciate the excellent technical assistance of Mrs. I. Knauer, Mrs. H. Waluk and Mrs. H. Siebke     

The effect of different Yersinia pestis antigens on the cellular link in immunity

Immunization with live plague vaccine has been shown to give no protection to thymectomized mice from subcutaneous challenge with Y. pestis virulent strain. Under the action of the vaccine or individual Y. pestis antigens (fraction I) the functional and morphological activation of thymocytes and macrophages is observed, more pronounced in C57BL/6 mice and less pronounced in CBA mice. Y. pestis antigenic preparations (fractions I and II, pesticin) act as T-cell mitogens and are thus capable of inducing the in vitro proliferation of thymocytes. At the same time the in vivo action of fraction II induces a decrease in the level of lymphocytes in the peripheral blood of mice and the destruction of lymphocytes in their thymus and spleen.     

Tumor necrosis factor-independent protective effect of recombinant IFN-gamma against acute toxoplasmosis in T cell-deficient mice

rIFN-gamma conferred remarkable resistance against acute infection with Toxoplasma gondii in T cell-deficient (athymic nude) mice. Mice that received an i.p. injection of rIFN-gamma every other day beginning 24 h before infection for a total of eight doses survived significantly longer than untreated control mice although all of the treated mice died after the lymphokine was discontinued. Mice that received 14 doses of rIFN-gamma survived significantly longer than those that received eight doses of the lymphokine although mice started dying soon after the final (14th) injection of rIFN-gamma and eventually all of the treated mice died. Histologic study revealed that the IFN-gamma treatment prevented proliferation of the organisms in all organs examined, including brain, lung, heart, liver, and spleen. The treatment was effective even when started 1 day after infection. Peritoneal macrophages obtained from mice injected with rIFN-gamma were activated and effectively killed tachyzoites of T. gondii in vitro. TNF activity could not be detected in sera of the infected mice during treatment with rIFN-gamma. Administration of anti-TNF antibody did not affect the protective effect of rIFN-gamma against T. gondii infection. These facts indicate that rIFN-gamma can confer resistance to acute infection with T. gondii without collaboration of lymphokines derived from T cells and TNF. This suggests that rIFN-gamma may be effective for therapy of toxoplasmosis in immunosuppressed patients who have impaired activity of T cell function, especially those with AIDS.     

A novel in vivo follicular dendritic cell-dependent iccosome-mediated mechanism for delivery of antigen to antigen-processing cells

Recent scanning electron microscopic studies on isolated follicular dendritic cells (FDC) showed that dendrites of certain FDC were "beaded," i.e., consisting of a series of interconnected immune complex coated bodies (termed "iccosomes," measuring 0.3 to 0.7 micron diameter). In vitro these iccosomes detach from one another with ease. The major objectives herein were to establish whether these structures can be detected in sections and whether iccosomes serve to disseminate antigen in vivo. Beginning at day 1, the time point used for isolating beaded FDC, the popliteal lymph nodes of immune C3H mice were studied with light and transmission electron microscopy for 2 wk (i.e., at days 1, 3, 5, 8, and 14) after hind footpad injection of the histochemically detectable antigen, horseradish peroxidase (HRP). Iccosomes (0.25 to 0.38 micron diameter), contoured by a peroxidase (PO)-positive coat of HRP-anti-HRP complexes, were first detected by transmission electron microscopy at day 1 adjacent to cell bodies of certain FDC. Within their limiting membrane they contained flocculent material that was PO positive. At day 3 by light microscopy, germinal centers were seen enlarged and the antigen-retaining reticulum, composed of antigen-bearing FDC, appeared diffuse. This coincided with the transmission electron microscopic visualization of a dispersed state of iccosomes among the follicular lymphocytes. At that time iccosomes were seen attached to the surface of lymphocytes via PO-positive immune complexes and were surrounded by microvillous processes of these cells. Germinal center lymphocytes and tingible body macrophages both responded to contact with iccosomes by endocytosis. Antigen-containing tingible body macrophage were most conspicuous by light microscopy at day 5, when transmission electron microscopy showed that the majority of germinal center lymphocytes contained endocytosed HRP in secondary lysosome-like granules associated with the Golgi apparatus. The number of dispersed iccosomes was markedly reduced by day 5. In controls injected with HSA, a PO-negative antigen, lymphocytes and tingible body macrophages were PO-negative. The presence of antigen in both cell types was confirmed through the use of a gold-conjugated antigen (goat IgG). Simultaneous immunoperoxidase labeling of the same tissues with anti-Ia showed the gold conjugate containing B cells to be Ia+. Antigen-positive B cells and tingible body macrophages were greatly reduced in numbers by day 14, suggesting the intracellular fragmentation of the antigen.(ABSTRACT TRUNCATED AT 400 WORDS)     

Toxoplasma gondii: Effect of maternal infection in the development of lymphoid organs of BALB/c neonates

Toxoplasmosis is one of the worldwide parasitic zoonoses. Alterations in the lymphopoietic system are still poorly studied. We analyzed lymphoid organs of BALB/c mice neonates from Toxoplasma gondii-intraperitoneally-infected mothers on 19th day of gestation, with 30 tachyzoites of strain RH. Normal non-infected pregnant females were used as controls. At 7 days after birth, animals were classified as neonates from infected (NIM) and neonates from non-infected mothers (NNIM). Weight of the thymus and number of thymic cells in NIM were decreased, percentage of apoptosis was significantly increased. Decrease in lymphocytes and monocytes and an increase of plasma cells were observed in bone marrow of NIM. Peripheral blood of NIM showed an increase of monocytes and neutrophils and a decrease in lymphocytes. Infection of the mother during the last day of gestation provokes in the neonates changes in the lymphoid organs that could explain survival of 75% of them.     

Immunoregulation in experimental disseminated histoplasmosis: flow microfluorometry (FMF) studies of the Thy and Lyt phenotypes of T lymphocytes from infected mice

Previous studies have shown that mice infected i.v. with 6 X 10(5) yeast phase Histoplasma capsulatum (Hc) develop suppressed immune responses during weeks 1 to 4 of infection but that by weeks 8 to 12 of infection these responses return to normal. In this study total and differential cell counts showed that as early as the third day of infection there was a marked reduction in the number of lymphocytes recovered from the peripheral blood, bone marrow, and thymus of infected animals. Concomitantly, there was an increase in the number of splenic lymphocytes. By day 28 both the total and differential cell counts were similar in both infected and normal animals. Flow microfluorometric (FMF) studies comparing the Thy-1.2, Lyt-1, Lyt-2, and surface immunoglobulin (slg) phenotypes of lymphocytes from normal and infected mice were performed. Between days 5 and 7 the thymocytes from infected mice displayed a higher relative fluorescence intensity (RFI) of the Thy-1.2 marker than normal thymocytes, whereas at day 10, the RFI was less than that of normal thymic lymphocytes. Between days 7 and 10 of infection the RFI of the Lyt-2 marker was less on thymocytes from Hc-infected mice; however, there was no change in the Lyt-1 marker. Examination of these lymphocyte markers in blood, spleen, and mesenteric lymph nodes showed that there were decreases in the RFI of both the Thy-1.2 and Lyt-2 between days 5 and 10 of infection. No changes were observed in the Lyt-1 or slg markers. By day 28 there were no differences between the normal and infected mice with respect to any surface marker in any of the organs studied. In other experiments, the effect of adrenalectomy before infection on these surface markers was studied. Absolute numbers of Thy-1.2+, Lyt-1+, and Lyt-2+ cells were significantly increased in the spleen and significantly decreased in the thymus and peripheral blood of infected mice relative to normal controls. These studies suggest that there is a migration of cells from the thymus, blood, and bone marrow to the spleens of mice with disseminated Hc infection.     

Perforin mediated apoptosis of cerebral microvascular endothelial cells during experimental cerebral malaria

Cerebral malaria is a serious complication of Plasmodium falciparum infection. We have investigated the role of perforin in the pathogenesis of cerebral malaria in a murine model (Plasmodium berghei ANKA (PbA) infection). C57BL/6 mice demonstrated the typical neuropathological symptoms of experimental cerebral malaria infection from day 5p.i. and became moribund on day 6p.i. This pathology was not seen in PbA-infected, perforin-deficient (pfp-/-) mice. From days 5-6p.i. onwards there was a significant increase in mRNA for granzyme B and CD8, but not CD4, in brain tissue from PbA-infected C57BL/6 and pfp-/- mouse brains. Perforin mRNA was strongly increased in the brains of PbA-infected C57BL/6 mice on day 6p.i. Immunohistochemistry revealed increased perforin staining and elevated numbers of CD8(+) cells within the cerebral microvessels in PbA-infected C57BL/6 at days 5 and 6p.i. compared with uninfected animals. At day 6p.i., there were TUNEL-positive cells and activated caspase-3 positive cells of endothelial morphology in the CNS of PbA-infected C57BL/6 mice. The TUNEL-positive cells were greatly reduced in pfp-/- mice. These results suggest that CD8(+)T lymphocytes induce apoptosis of endothelial cells via a perforin-dependent process, contributing to the fatal pathogenic process in murine cerebral malaria.     

Quantitative comparison of infection of neural cell and fibroblast monolayers by two strains of Toxoplasma gondii

Disease caused by the coccidian Toxoplasma gondii can be confined to the central nervous system, although the parasite is capable of infecting all organ systems. To determine whether neural cells are differentially susceptible to infection and destruction by T. gondii, infection of neonatal mouse brain monolayers was compared to infection of human fibroblast monolayers under the same conditions with equal inocula of two parasite strains. In preliminary experiments there was no difference in total parasite yield or in plaques per monolayer between rodent and human cells. A standardized inoculum of T. gondii RH strain caused 35.6 +/- 6.4 (SD) plaques per well in neural explant monolayers compared to 39.3 +/- 12.5 plaques per well in fibroblasts. T. gondii P strain produced 35.6 +/- 8.9 infected foci per well in neural cells compared to 32.6 +/- 9.3 foci in fibroblasts. Intrinsic properties of neural cells do not appear to cause a higher rate of infection than that in nonneural cells.     

CD8+ T cells mediate recovery and immunopathology in West Nile virus encephalitis

C57BL/6J mice infected intravenously with the Sarafend strain of West Nile virus (WNV) develop a characteristic central nervous system (CNS) disease, including an acute inflammatory reaction. Dose response studies indicate two distinct kinetics of mortality. At high doses of infection (10(8) PFU), direct infection of the brain occurred within 24 h, resulting in 100% mortality with a 6-day mean survival time (MST), and there was minimal destruction of neural tissue. A low dose (10(3) PFU) of infection resulted in 27% mortality (MST, 11 days), and virus could be detected in the CNS 7 days postinfection (p.i.). Virus was present in the hypogastric lymph nodes and spleens at days 4 to 7 p.i. Histology of the brains revealed neuronal degeneration and inflammation within leptomeninges and brain parenchyma. Inflammatory cell infiltration was detectable in brains from day 4 p.i. onward in the high-dose group and from day 7 p.i. in the low-dose group, with the severity of infiltration increasing over time. The cellular infiltrates in brain consisted predominantly of CD8(+), but not CD4(+), T cells. CD8(+) T cells in the brain and the spleen expressed the activation markers CD69 early and expressed CD25 at later time points. CD8(+) T-cell-deficient mice infected with 10(3) PFU of WNV showed increased mortalities but prolonged MST and early infection of the CNS compared to wild-type mice. Using high doses of virus in CD8-deficient mice leads to increased survival. These results provide evidence that CD8(+) T cells are involved in both recovery and immunopathology in WNV infection.     

Viral infection of the thymus.

We have examined infection of the thymus during congenitally acquired chronic lymphocytic choriomeningitis virus (LCMV) infection of mice, a classic model of antigen-specific T-cell tolerance. Our results show that (i) infection starts at the fetal stage and is maintained throughout adulthood, and (ii) this chronic infection of the thymus can be eliminated by transfer of virus-specific cytotoxic T lymphocytes (CTL) that infiltrate the thymus and clear all viral products from both medullary and cortical regions. Elimination of virus from the thymus results in abrogation of tolerance. During the fetal stage, the predominant cell type infected is the earliest precursor of T cells with a surface phenotype of Thy1+ CD4- CD8- J11d+. In the adult thymus, infection is confined primarily to the cortisone-resistant thymocytes present in the medullary region. The infected cells are CD4+ and J11d+. The presence of J11d, a marker usually associated with immature thymocytes, on infected single positive CD4+ "mature" thymocytes is intriguing and suggests that infection by this noncytolytic virus may affect development of T cells. There is minimal infection of the CD8+ medullary thymocytes or of the double positive (CD4+ CD8+) cells present in the cortex. Infection within the cortex is confined to the stromal cells. Interestingly, there is infection of the double negative (CD4- CD8-) thymocytes in the adult thymus, showing that even during adulthood the newly developing T cells are susceptible to infection by LCMV. Virus can be eliminated from the thymuses of these carrier mice by adoptive transfer of medullary region first and then from the thymic cortex. This result clearly shows the need to reevaluate the widely held notion that mature T cells are unable to reenter the thymus. In fact, in our experiments the donor T cells made up to 20 to 30% of the total cells in the thymus at 5 to 7 days after the transfer. The number of donor T cells declined as virus was eliminated from the thymus, and at 1 month posttransfer, the donor T cells were hardly detectable. The results of this study examining the dynamics of viral infection and clearance from the thymus, the primary site of T-cell development, have implications for understanding tolerance induction in chronic viral infections.     

T cell phenotype and intracellular IFN-gamma production in peritoneal exudate cells and gut intraepithelial lymphocytes during acute Toxoplasma gondii infection in mice

Although there are many reports on the splenic (systemic) T cell response after Toxoplasma gondii infection, little information is available regarding the local T cell responses of peritoneal exudate cells (PEC) and gut intraepithelial lymphocytes (IEL) following peroral infection with bradyzoites. Mice were infected with 40 cysts of the 76K strain of T. gondii, and then sacrificed at days 0, 1, 4, 7 and 10 postinfection (PI). The cellular composition and T cell responses of PEC and IEL were analyzed. The total number of PEC and IEL per mouse increased after infection, but the ratio of increase was higher in IEL. Lymphocytes were the major component of both PEC and IEL. The relative percentages of PEC macrophages and neutrophils/eosinophils increased significantly at day 1 and 4 PI, whereas those of IEL did not change significantly. The percentage of PEC NK1.1 and gamma delta T cells peaked at day 4 PI (p < 0.0001), and CD4 and CD8 alpha T cells increased continuously after infection. The percentages of IEL CD8 alpha and gamma delta T cells decreased slightly at first, and then increased. CD4 and NK1.1 T cells of IEL did not change significantly after infection. IFN-gamma-producing PEC NK1.1 T cells increased significantly from day 1 PI, but the other T cell subsets produced IFN-gamma abundantly thereafter. The proportion of IEL IFN-gamma-producing CD8 alpha and gamma delta T cells increased significantly after infection, while IEL NK1.1 T cells had similar IFN-gamma production patterns. Taken together, CD4 T cells were the major phenotype and the important IFN-gamma-producing T cell subsets in PEC after oral infection with T. gondii, whereas CD8 alpha T cells had these roles in IEL. These results suggest that PEC and IEL comprise different cell differentials and T cell responses, and according to infection route these factors may contribute to the different cellular immune responses.     

Histological changes of the mouse thymus during involution and regeneration following administration of hydrocortisone

Summary A histological study has been made of the thymus in mice during acute involution and regeneration following administration of hydrocortisone. The cortex undergoes remarkable changes in the microscopic structure during involution and regeneration. During involution the lymphocytes in the cortex rapidly decrease and are removed. Then a rapid replacement of lymphocytes occurs during regeneration. On the basis of formation and repopulation of lymphocytes the regenerative process of the cortex is divided into seven phases. The reconstitution of the cortex proceeds more rapidly in females than in males. Newly formed lymphocytes take origin from the mesenchymal cells in the cortex. Such mesenchymal cells become distinguishable from epithelial reticular cells during involution. They appear to engulf destroyed lymphocytes and debris during involution and then transform into immature lymphoid cells during early regeneration. The findings may support the recent reutilization concept that destroyed lymphocytes are phagocytized and reutilized by reticular cells in heteroplastic differentiation into immature lymphoid cells. In the cortex PAS-positive sudanophilic cells which are derived from the perivascular and subcapsular connective tissue appear with involutionary changes. They become gradually reduced again with progress of the regeneration of the cortex. During involution the medulla are temporarily filled with lymphocytes migrated from the cortex. The epithelial reticular cells in the medulla are found grouped in cords or clumps in the severely involuted thymus. In the medulla there are two types of PAS-positive epithelial reticular cells; one contains a large, colloid-like, PAS-positive inclusion within the cytoplasm and the other has cytoplasm diffusely filled with PAS-positive substance. During involution and early regeneration, the former type increases while the other shows almost no significant changes. Hassall's corpuscles somewhat increase in frequency during involution and early regeneration.     

斜带石斑鱼胸腺的显微和超微结构

本文通过解剖及组织切片技术、光学显微镜、透射和扫描电子显微镜技术,对斜带石斑鱼(Epinephelus coioides)胸腺器官组织进行了观察研究。结果表明:斜带石斑鱼胸腺实质主要由胸腺细胞(淋巴细胞)和网状上皮细胞构成。鱼体从Ⅰ龄之后,其胸腺发生明显的变化,与幼鱼有所不同,主要是胸腺可明显区分为三个区域:胸腺外皮质区、内皮质区和髓质区。外皮质区主要由网状上皮细胞、黏液细胞、成纤维细胞和少量淋巴细胞构成,细胞排列疏松;内皮质区主要由密集的淋巴细胞和网状上皮细胞组成,以含有大量的淋巴细胞为特征;髓质区主要由淋巴细胞和较多的网状上皮细胞构成,总体特征是淋巴细胞数量比内皮质区的少,且细胞排列较疏松。外皮质区、内皮质区相当于高等脊椎动物的皮质;髓质区相当于高等脊椎动物的髓质。髓质区之下有结缔组织,在Ⅱ龄以上的成体出现胸腺小体(Hassall's corpuscles)或类似胸腺小体的结构,而且随着年龄的增加,胸腺外皮质区增厚,结缔组织增加,还表现在内皮质区和髓质区组织逐渐萎缩变薄,胸腺的细胞组成类型和淋巴细胞数量上有所变化等等。这些现象在Ⅱ龄鱼开始出现,即胸腺呈现退化迹象,在Ⅲ龄以上鱼体呈现明显的退化和萎缩。胸腺表面扫描电镜结果表明:其上皮细胞表面具有微嵴以及由微嵴组成的指纹状结构,有一些微孔分布。透射和断面扫描电镜的结果进一步表明:胸腺组织内的细胞成分复杂,除了淋巴细胞和网状上皮细胞外,还具有巨噬细胞、肥大细胞、肌样细胞、浆细胞、指状镶嵌细胞和纤维细胞等。     

Localization of terminal deoxynucleotidyl transferase (TdT) in rat thymus using immunoperoxidase methods

Summary Indirect and peroxidase anti-peroxidase (PAP) immunoenzymatic methods were used to detect terminal deoxynucleotidyl transferase (TdT) in imprints and formalin-fixed paraffin sections of normal rat thymus. TdT is found in the nuclei of small lymphocytes in imprint samples from neonatal and adult rat thymus, showing granular or circular patterns of peroxidase reaction products. Diffuse brown reaction products of peroxidase are located in both the nuclei and cytoplasm of medium and large lymphocytes. Indirect measurements show that, as age progresses, the percentage of peroxidase-positive cells decreases in all types of lymphocytes, from 72.4% on the 11th day to 54.8% in the 5th month, whereas that of negative cells increases from 14.4% to 39.4%. In formalin-fixed paraffin sections, peroxidase-positive lymphocytes are found mainly in the cortex and cortico-medullary boundary, and only rarely in the medulla.     

Sequential analysis of cell differentials and IFN-gamma production of splenocytes from mice infected with Toxoplasma gondii

To assess the relationship between the changes of cellular components and the production of Th1 cytokine in the immune tissue, inbred C57BL/6 mice were orally infected with 40 cysts of 76K strain of Toxoplasma gondii. The sequential change of cell differentials and IFN-gamma production of splenocytes were analyzed by Diff-Quik stain and RT-PCR. There were no significant proportional changes of cellular components of splenocytes until day 4 postinfection (PI) as compared to those of day 0, and the relative percentage of macrophages and neutrophils/eosinophils increased significantly (p < 0.01) thereafter. The expression of IFN-gamma mRNA of CD3- cells was observed from day 1 PI at a low level. However, IFN-gamma production of CD3+ cells increased significantly from day 4 PI (p < 0.01) which progressively increased thereafter. These findings provide the relative percentages of granulocytes and macrophages were increased in conjunction with increase of total number of splenocytes after oral infection with T. gondii in the susceptible murine hosts, and lymphocytes were the major cellular components and the important source of IFN-gamma.     

Ontogeny of lymphocytes expressing J chain in chickens

The ontogeny of chicken lymphocytes expressing J chain (LEJ) was investigated in the embryonic bursa of Fabricius, the spleen, and the thymus. Simultaneous appearance of LEJ was detected in the bursa and spleen on Day 14 of incubation. These cells were detected later in the thymus. The LEJ were found to increase rapidly in the spleen from the 19th to 20th incubation day. In adult chickens, the highest percentage of LEJ was also found in the spleen. These cells were seen in the thymus at a lower frequency. Intermediate numbers were found in bursal and peripheral blood lymphocytes. The frequencies of the LEJ were similar to those of lymphocytes positive for cytoplasmic immunoglobulins (Ig) IgA and IgM, but were not related to the number of lymphocytes expressing surface Ig. It is possible to consider that the suitable site for LEJ is the spleen, on the basis of the rapid increase in the number of LEJ just before hatching and from the fact that the highest value is found in adult chickens. Furthermore, LEJ may participate in secretion of IgA or IgM but not be associated with the expression of surface Ig.     

Potentiation of autoimmune response in rats infected with Toxoplasma gondii. Effect of the infection route

The aim of this report is to describe the influence of the way of infection with 3 X 10(3) trophozoites of Toxoplasma gondii on the auto- and heteroimmune responses of rats immunized with chemically modified rat male accessory glands (MRAG) and human serum albumin (HSA) 6 and 36 days after infection. The delayed hypersensitivity (DTH) response to MRAG was potentiated in rats infected in thymus proximity (p less than 0.02) when compared with rats only immunized. The parasites introduced intraperitoneally did not modify the cellular autoimmune response. The titers of hemagglutinating antibodies to MRAG were increased in animals infected by both ways (p less than 0.05). The response to HSA did not show significant difference between the infected and uninfected rats. Thymic involution and proliferation of lymphocytes and plasma cells were observed at 6 and 52 days post-infection only in rats infected in thymus proximity (p less than 0.05). A correlation between the potentiation of cellular autoimmune response and the injection of parasites in thymus proximity was observed.     

Autoimmune reactions against liver cells by syngeneic neuraminidase-treated lymphocytes.

We have found that the entrapment of neuraminidase-treated lymphocytes in the liver leads to the induction of autoimmune cellular cytotoxic reactions. Lymphocytes from mouse spleen and thymus were incubated with neuraminidase in vitro and injected i.v. into syngeneic recipients. Lymphocytic infiltrations into the liver were seen 7 days later with both types of cells. After repeated weekly injections of asialo-lymphocytes, destruction of liver tissue became apparent. Electron-microscopic studies showed that hepatocytes, fat storage cells, and endothelial cells were affected, mainly at the hepatic periphery. It is concluded that the adhesion of asialo-lymphocytes to liver cells induces their cytotoxic activity. Similar reactions may occur after paramyxovirus infection due to the action of viral neuraminidase.     

Pathogenicity of selected Toxoplasma gondii isolates in young pigs

The pathogenicity in 7-week-old pigs to five different Toxoplasma gondii strains of various host species origin was compared after i.v. inoculation of 10(4) tachyzoites. Additionally, one group of pigs was inoculated i.v. with 10(6) tachyzoites of the reference strain, SSI 119. In response to the infection a significant effect of T. gondii tachyzoite inoculation dose as well as differences among strains could be observed in several parameters. The 10(6)-dose inoculated pigs showed variable degrees of clinical illness and recurrent episodes of fever 4-17 days p.i., while pigs of four of the 10(4) tachyzoite inoculated groups experienced a short-lived rise in body temperature from day 6-8 p.i. without any apparent illness or inappetence. Control pigs and pigs infected with the least pathogenic strain had normal body temperature throughout the experiment. In all inoculated pigs, T. gondii-specific IgM and IgG antibodies appeared from day 8-10 and 10-17 p.i., respectively. Serum levels of alkaline phosphatase and the acute phase protein haptoglobin were decreased or increased, respectively, in response to the infection. Differential leukocyte count on peripheral blood revealed a significant lymphocytopenia on day 6 p.i. equal to both CD4+ and CD8+ T-cells, but shifting towards a reduced ratio of CD4+/CD8+ T-cells from day 8-14 p.i. In the 10(6)-dose inoculated pigs a considerable increase in zymosan induced and spontaneous oxidative burst capacity of peripheral blood leukocytes was observed from 6 days p.i. compared with control pigs. Oxidative burst capacity was not examined for other pigs. In conclusion, several useful parameters to identify differences in T. gondii pathogenicity other than mortality were identified. Furthermore, even at low doses, significant differences between recently collected Danish T. gondii field isolates were demonstrated after i.v. inoculation in young pigs.     

The immunoproliferative response of mice to intravenously or subcutaneously injected BCG

Summary Intravenous injection of BCG caused (1) a transient thymic epithelial hyperplasia with increase of PAS-positive cells in the cortex and medulla which showed the pronounced secretory activity of a substance which could be histochemically identified as an acid mucopolysaccharide; (2) an equally transient increase in the number of pyroninophilic lymphocytes with increased polyribosome content of the cells and mitoses in the thymic cortex; this reached a peak on day 6 following the injection but was unassociated with an increase in thymic weight; and (3) a systemic granulomatous histiocytic reaction in the liver, spleen, lungs, and lymph nodes, but not in the thymus, bone marrow, or Peyer's patches. The significance of the thymic epithelial changes is not clear but it did coincide with increased pyroninophilia and mitotic activity of the thymic cortical cells, suggesting a possible interaction between this secretory product and the thymic cortex. Comparing the thymic changes with the thymus of other animals of the same species injected with i.v. or i.p. LPS, i.v. or s.c. HIU II fraction of BCG, i.v. pertussis vaccine, i.p. complete or incomplete Freund's adjuvant, and killed at the same planned intervals after the injection of the adjuvants, BCG proved to have a unique action on the thymus with regard to both lymphocytic and epithelial changes. Hepatic, pulmonary, and splenic histiocytic granulomas were observed only in those animals injected intravenously with BCG.