Systemic Mycobacterium kansasii infection and regulation of the alloantigenic response.

Specific-pathogen-free B6D2 F1 hybrid mice were infected intravenously with 10(7) to 10(8) viable Mycobacterium kansasii cells. The growth of the five test strains in vivo was correlated with the level of delayed hypersensitivity to a cytoplasmic protein antigen injected into the footpad. M. kansasii TMC no. 1201 and 1203 gave rise to persisting systemic infections with an early delayed hypersensitivity response (day 7) followed by a profound anergy to the cytoplasmic protein antigen injections. Strains 1204, 1214, and 1217 declined in viability relatively rapidly and failed to induce detectable levels of delayed hypersensitivity. Spleens harvested from mice infected 20 to 30 days earlier with 10(8) M. kansasii 1203 cells contained a T-cell subpopulation capable of suppressing mixed lymphocyte reactions between normal B6D2 and C3H(He) cells. On the other hand, splenic T-cells taken from M. kansasii 1214-infected mice enhanced, rather than suppressed, the indicator mixed lymphocyte reactions. The kinetics of stimulator-suppressor T-cell production within the spleens of the heavily infected mice differed as the two contrasting M. kansasii infections progressed. Such cellular interactions could well be responsible for the observed persistence of the systemic M. kansasii 1203 infection.     

Immune responsiveness in mice heavily infected with Mycobacterium kansasii.

Growth of Mycobacterium kansasii TMC 1203 in B6D2 F1 hybrid mice was associated with increased splenic cellular proliferation, hyperplasia and the generation of non-specific antibacterial resistance. Both responses were dose dependent; the larger the inoculum, the more rapid and extensive the cellular response. However, such mice were still unable to reduce the mycobacterial load within the tissues, apparently because of their inherent resistance to inactivation by immunologically activated macrophages. On the other hand, mice infected with the non-persistent strain of M. kansasii 1214 exhibited only a transient increase in non-specific (anti-listeria) resistance which rapidly declined as the number of viable mycobacteria within the spleen fell below an arbitrary threshold level. Mice infected with either M. kansasii 1203 or 1214 could be immunized with sheep red blood cells (SRBCs), an unrelated T cell-dependent antigen. The humoral (PFC) response was not affected by the mycobacterial load within the spleen. However, the delayed footpad swelling reaction was severely depressed. The latter could be restored merely by increasing the size of the intravenous sensitizing inoculum 100-fold. The present study indicates that mice chronically infected with M. kansasii are not severely immunosuppressed (as had been inferred from earlier in vitro lymphoproliferation studies) but are fully capable of responding to appropriate in vivo stimuli.     

Adoptive transfer of acquired resistance to Mycobacterium kansasii by T cells harvested from chronically-infected mice.

Growth of Mycobacterium kansasii in intravenously infected mice ceases when the spleen cells express an enhanced non-specific resistance to a secondary challenge. Mice inoculated with 10(6) CFU M. kanasii 1203 develop a population of splenic T cells which are able to transfer protection passively to sublethally-irradiated syngeneic recipients when challenged with M. kansasii. Although the T-cell activated macrophages were unable to eliminate the mycobacteria from the spleen, they were able to prevent further growth of the organism in vivo. When mice which lack T cells (congenitally athymic, or 'nude' mice) were infected with M. kansasii, the cellular defences were unable to halt the progressive growth of the challenge organisms within the tissues. When normal mice were inoculated with large numbers of viable M. kansasii 1203 (up to 5 X 10(7) CFU), the activated macrophages within the spleen were capable of limiting the further growth of the bacterial population in vivo, but with no T-cell response capable of adoptively immunizing naive recipients against a secondary M. kansasii challenge. Thus, it seems likely that M. kansasii can induce the formation of activated macrophages by two separate mechanisms: one is a T-cell dependent process which occurs in mice inoculated with moderate doses (10(6) CFU) of M. kansasii, while the other is T-cell independent and occurs when a large infectious inoculum is employed.     

Mitogenic activity of soluble preparations from Plasmodium berghei-infected erythrocytes to L3T4+, Lyt2- and L3T4-, Lyt2+ T-cell subsets

The mitogenic activity of soluble preparations of Plasmodium berghei-infected erythrocytes (PBEP) in cultures of T or non-T cells isolated from spleens of naive mice was investigated. The proportion of cells at each phase in the cell cycle was examined by flow cytometry after incubation with various concentrations of PBEP; the proliferation index (PI-cell numbers at S, G2 and M phases/cell numbers at all phases x 100) was calculated. An addition of PBEP led to significant increases in the PI levels of T cells, but not in those of non-T cells. Moreover, when PBEP were added to L3T4+, Lyt2- (helper) or L3T4-, Lyt2+ (suppressor) T-cell fractions separated from rosette-forming T cells in spleens, significant increases in PI levels were detectable in both helper and suppressor T-cell cultures. These results indicate that PBEP have a mitogenic activity directed to both helper and suppressor T-cell fractions isolated from spleens of naive mice and that PBEP or Plasmodium parasites may in this way induce complicated immune responses during malaria infection.     

犬蛔虫（Toxocaracanis）对感染鼠的细胞免疫和IL－1、IL－2免疫调节作用的影响

应用犬蛔虫（Ｔ．ｃａｒｎｉｓ）的感染性虫卵口饲感染Ｃ３Ｈ／ＨｅＮ鼠，体外培养后观察脾细胞的免疫学变化。感染第１－４周的脾细胞用ＣｏｎＡ刺激，Ｔ细胞的增殖反应，ＩＬ－２的诱生均明显地受到抑制，而且感染鼠脾细胞抑制了正常鼠脾细胞对ＣｏｎＡ的反应。感染鼠的脾细胞经ＳｅｐｈａｄｅｘＧ－１０过柱后，Ｔ细胞则不显示被抑制作用。表明影响Ｔ细胞被抑制作用的是感染鼠的巨噬细胞。相反，感染第１－４周的鼠所产生的ＩｇＧ和ＩｇＭ等抗体的Ｂ细胞活性增强；用ＬＰＳ刺激巨噬细胞诱生的白介素（ＩＬ）ＩＬ－１也增多。     

Development of Suppressor T-Cells in Mycobacterium habana-Infected Mice

Mice were infected intravenously with increasing numbers of Mycobacterium habana (simiae serotype II), and the levels of delayed-type hypersensitivity to purified protein derivative and M. habana cytoplasmic protein antigen were determined after 14, 30, and 90 days. A footpad delayed-type hypersensitivity response was seen in 14-day-infected mice and was followed by a persisting anergy. T-cell-enriched suspensions collected 30 and 90 days into the infection (anergic donors) showed depressed transformation indexes after phytohemagglutinin and M. habana cytoplasmic protein antigen treatment in vitro. The corresponding B-cell mitogen (lipopolysaccharide) responses were not affected. Mixing experiments with T-cell-enriched suspensions from day-90 M. habana-infected donors adoptively suppressed lymphocyte transformation by normal and day-14 spleen cells. This effect could be ablated by anti-theta serum and complement treatment of the day-90 cells, indicating that the lack of in vitro responsiveness to cytoplasmic protein antigen was mediated by a population of suppressor T-cells present in the heavily infected spleens. There was no evidence that similar cells were present in the spleens of the 14-day-infected animals. Suppressor T-cells could be induced in vitro by exposure of day-14 spleen cells to concanavalin A or M. habana cytoplasmic protein antigen before they were mixed with normal or day-14 indicator splenic lymphocytes. The timing of the appearance of suppressor T-cells in the infected spleens corresponded to a loss of footpad hypersensitivity by the M. habana-infected animals.     

CD4+ cells play a limited role in murine lung infection with Mycobacterium kansasii

Mycobacterium kansasii has emerged as an important nontuberculous mycobacterium that can cause severe infection in the immunocompromised host, especially in human immunodeficiency virus-infected patients. However, little is known about the pathogenesis of this infection. Because patients suffering from M. kansasii infection are severely compromised in their cellular immune response, we studied the course of infection in CD4+ cell knockout (KO) mice. Wild-type (WT) mice and CD4+ KO mice were infected with 10(5) cfu of M. kansasii. Although previously shown to be susceptible to Mycobacterium tuberculosis infection, CD4+ KO mice demonstrated no impairment in clearing infection with M. kansasii when compared with WT animals, despite reduced pulmonary inflammation (reduced granuloma formation and lymphocyte infiltration in the lungs). Pulmonary IFN-gamma levels and M. kansasii-induced IFN-gamma production by splenocytes from infected animals were reduced in CD4+ KO mice, confirming that these mice were defective in the M. kansasii-specific T helper cell type 1 immune response. Furthermore, mice deficient for IFN-gamma, IL-12p35, IL-12p40, or IL-18 also displayed a normal host defense against pulmonary infection with M. kansasii. These data suggest that CD4+ cells, IFN-gamma, and an intact T helper cell type 1 response play a limited role in protective immunity against pulmonary M. kansasii infection.     

The effect of combined chemotherapy on suppressor T-cell activity in Mycobacterium simiae-infected mice.

Specific pathogen-free B6D2 mice were infected with 10(6) or 10(8) viable Mycobacterium bovis (BCG Pasteur) or Mycobacterium simiae and the in vivo growth curves were correlated with the levels of delayed hypersensitivity developed against a cytoplasmic protein antigen (CPA) injected into a hind footpad at increasing time intervals after infection. Half of the heavily infected, anergic mice were placed on a regimen of 10 mg of rifampin, 5 mg of amikacin and 2 mg of clofazimine per 100 ml of drinking water 2 or 8 weeks into the infection. The number of viable mycobacteria recovered from the lungs and spleens of the treated mice (compared with the corresponding drug-free controls) were reduced by up to 10,000-fold over a 3-month treatment period. Spleen cells were harvested at increasing time intervals from the drug-treated and control mice and T-cell enriched suspensions were tested for blastogenic responsiveness to phytohaemagglutinin (PHA) and to the specific CPA mitogen. The early (day 14) peak in tritiated thymidine ([3H]-TdR) uptake was followed by a sharp drop to near background levels. Cell-mixing experiments demonstrated the presence of a suppressor T-cell population in the heavily infected spleens of the M. simiae-infected mice. The suppressor-cell effect was substantially reduced following combined drug therapy although the specific CPA-mediated response was less affected than the non-specific PHA-mediated response.     

Protective immunity in murine histoplasmosis: functional comparison of adoptively transferred T-cell clones and splenic T cells.

In this study, I examined whether a murine T-cell line and three clones that recognize Histoplasma capsulatum antigens in vitro could confer protection in vivo against a challenge of Histoplasma yeasts. C57BL/6 mice were each inoculated with 5 X 10(4) yeasts intravenously; 1 h later, 5 X 10(6) or 2 X 10(7) resting T cells were inoculated intravenously. At week 1 of infection, the T-cell line and all clones failed to reduce the number of H. capsulatum CFU in the spleens of mice compared with numbers in infected controls. Administration of recombinant interleukin 2 or cyclophosphamide to infected mice did not potentiate the functional activity in vivo of either the T-cell line or the clones. In contrast, inoculation with 2 X 10(7) CD4+ but not CD8+ cells isolated from the spleens of mice immunized with 10(6) viable yeast cells sharply diminished the number of CFU in the spleens of infected animals. Moreover, splenic CD4+ cells from immune mice transferred a delayed-type hypersensitivity response, whereas the T-cell line and clones did not. Injection Injection of an equal number of cloned T cells and CD8+ splenocytes from immune mice did not transfer resistance to infected mice. Additional studies were undertaken to determine if the ineffectiveness of cloned T cells was associated with a failure to migrate to and survive within spleens of infected mice. B6.PL Thy-1a/Cy mice, which are genetically identical to C57BL/6 mice except that T cells of the former bear Thy-1.1 rather than Thy-1.2, were inoculated with Histoplasma yeasts and then injected with immune CD4+ splenocytes or a T-cell clone. At days 1 and 7 of infection, virtually no Thy-1.2+ cells were detected in the spleens of infected mice given cloned T cells. However, the spleens of animals inoculated with immune CD4+ cells contained a small but significant (P less than 0.01) proportion of Thy-1.2+ cells at both day 1 and day 7 postinoculation of H. capsulatum. Thus, the failure of T-cell clones to transfer protection against H. capsulatum may be explained by defective trafficking or poor survival in vivo or both.     

Demonstrations of a B-Cell Population That Regulates the Immune Response in Spleens of Mice Infected with Herpes Simplex Virus Type I

A population of B cells that regulates the immune response was demonstrated in splenic mononuclear cells (SMNC) from mice infected with herpes simplex virus type 1 (HSV). SMNC, obtained from mice 3 days after HSV infection at a dose of 100 LD₅₀, exhibited a reduction in the proliferative response of naive SMNC stimulated with various lectins or allogeneic lymphocytes in a 5-day mixed lymphocyte reaction. Cocultivation of naive SMNC with phagocytic cell-free SMNC (Mφ^-MNC) from infected mice resulted in the inhibition of lymphocytic blast transformation stimulated with various lectins. These cells were characterized as nylon-wool adherent cells that were eliminated by treatment with anti-Ig antiserum, but not anti-Thy 1.2 monoclonal antibody or anti-asialo GM₁ antiserum, followed by complement treatment. In addition, the suppressor cell activity was not demonstrated in Mφ^-MNC obtained from HSV-infected CBA/CaHN-xid/J mice, which contain a congenital B-cell deficiency. These results suggest that, in addition to suppressor T cells, a population of B cells, which can inhibit lymphocyte proliferations upon stimulation with lectins and alloantigens, might be generated in spleens of mice following HSV infections.     

Effect of chemotherapy on suppressor T cells in BCG-infected mice.

Specific pathogen-free B6D2 mice infected intravenously with 10(6) or 10(8) viable BCG Pasteur develop an anti-tuberculous immune response resulting in a progressive decline in viable BCG counts for the spleen and lung. Mice infected with 10(8) bacilli did not develop detectable levels of tuberculin hypersensitivity. Spleen cells harvested from both groups of mice at increasing time intervals after infection were T-cell enriched by nylon wool passage and tested for blast transformation following exposure to PHA or PPD. An early peak in tritiated thymidine uptake was observed following PPD exposure of cells from both the 10(6) and 10(8) groups. Cells from the latter group of animals developed a profound suppression to responsiveness to PPD throughout the remainder of the experiment. If the heavily infected mice were exposed to a regimen of 10 mg isoniazid plus 10 mg rifampin per 100 ml of drinking water for 30 days, the viable BCG population present within the lungs and spleen declined to near undetectable levels. This drop was associated with a decline in supressor T-cell activity demonstrated by appropriate cell-mixing experiments in vitro. The blastogenic responses to both PHA and PPD were substantially restored after 30 days of drug treatment. Treatment of the BCG infected mice within the first 7 days of infection prevented the development of the suppressor T-cell population.     

Immunoregulation of genetically controlled acquired responses to Leishmania donovani infection in mice: demonstration and characterization of suppressor T cells in noncure mice

On a B10 genetic background, genes in the I region of H-2 influence the development of acquired T-cell mediated immunity to Leishmania donovani infection in mice. In previous studies, noncure in H-2d mice could be abrogated by pretreatments with cyclophosphamide or sublethal irradiation. The prophylactic effect of these pretreatments was consistent with deletion of the precursors of suppressor T cells suppressing T-cell-mediated immune responses. In this study, cell transfer experiments provide direct evidence for the role of suppressor T cells in the noncure response. T-cell-enriched populations isolated from the spleens of B10.D2/n mice infected 30, 61, or 85 days previously reversed the prophylactic effect of sublethal irradiation when injected before infection into B10.D2/n mice that had received 550 rads. B-cell-enriched populations failed to transfer suppression in this manner, and T-cell-enriched populations from the spleens of normal B10.D2/n mice had only a transient effect on liver parasite loads. Transfer of suppression with the T-cell-enriched populations from infected donors was abrogated by pretreatment with anti-Thy-1.2 and anti-Lyt-1.2 antisera plus complement but not by pretreatment with anti-Lyt-2.2 plus complement, indicating that the suppressor T cell involved has an Lyt-1+2- surface phenotype. Results are discussed in relation to the possible mechanism of H-2-linked control.     

Evidence for two distinct populations of suppressor cells in the spleens of Mycobacterium bovis BCG-Sensitized mice.

Spleen cells from female C57BL/6 mice infected intravenously with 1 mg (about 10(7) viable units) of bacillus Calmette-Guérin (BCG) were shown to suppress the blastogenic responses induced by the T-cell mitogens phytohemagglutinin and concanavalin A and by the B-cell mitogen lipopolysaccharide in spleen cells from normal syngeneic mice. By using various separation procedures or cellular treatments, evidence was found for two distinct populations of splenic suppressor cells. One population belonged to the monocyte-macrophage lineage on the basis of their adherence to plastic surfaces, their removal after treatment with carbonyl iron, and their resistance to gamma irradiation. The other population of suppressor cells belonged to the T lymphocytes due to their sensitivity to an anti-Thy 1 antiserum and complement and to gamma irradiation. After separation on nylon wool columns, inhibitory activity was found in both the nonadherent and the adherent spleen cell populations. Both populations of suppressor cells were present in the spleens 14 days after BCG inoculation and persisted for at least 40 days after infection.     

Development of suppressor T cells in mice heavily infected with mycobacteria

Specific pathogen-free B6D2 mice were infected intravenously with 10(8) viable BCG, M. habana or M. simiae and the level of tuberculin hypersensitivity to 2.5 micrograms PPD or cytoplasmic protein antigens (CPA) prepared from the other organisms was determined using the footpad swelling test with increasing time after infection. This was correlated with the growth or persistence of mycobacterial populations within the liver. Spleen cells were removed from these infected mice and the level of blast transformation following exposure to PHA, PPD or M. habana or M. simiae CPA was measured in vitro. Early in the mycobacterial infections (day 14) thymidine incorporation by the spleen cells was significantly enchanced followed by a profound depression in incorporation rates as the infection progressed. The mechanism of this depressed response involved the production of suppressor T cells in the spleen. In the case of the M. simiae or M. habana infection, cells capable of mediating suppression were still present even after 12 months of infection. In the BCG infection, suppressor T cells declined with time so that by 4 months incorporation rates were back to normal and suppressor cells were no longer detectable in the spleens of the infected animals.     

Restoration of suppressor function in athymic mice.

Antibody responses of normal and congenitally athymic (nu/nu) mice were measured to the phosphorylcholine determinant of a pneumococcal C-polysaccharide. The plaque-forming cell responses of athymic mice were approximately tenfold higher than for intact controls. This enhancement was equivalent to that obtained by treatment of controls with antithymocyte serum. In both cases, the enhanced responses presumably result from a lack of suppressor T cells. Reconstitution of athymic mice with normal thymocytes restored both suppressor and helper T cell functions. Whereas suppressor activity did not appear until 6 days after transplantation of T cells, helper activity was fully restored within 24 h and had diminished by 6 days.     

Trypanosoma cruzi-induced immunosuppression: blockade of costimulatory T-cell responses in infected hosts due to defective T-cell receptor-CD3 functioning.

A model of experimental Trypanosoma cruzi murine infection with chemically induced metacyclic forms (opossum clone Dm28c) showed a marked state of T-cell unresponsiveness during acute phase, but lacked evidence of suppressor cell activity. Spleen cells from infected mice were suppressed in vitro in responses to T-cell activators concanavalin A, anti-Thy1 monoclonal antibody (MAb), and anti-CD3 MAb compared with spleen cells from control littermates. Activation with accessory cell-independent stimulus provided by immobilized anti-CD3 was defective in splenic CD4-positive T cells from infected mice, but not in such cells from control mice. No evidence of splenic suppressor cell activity was found in cell-mixing experiments using nylon-passed T cells from control and infected donors. Kinetic experiments showed that there was a discrete stage in infection when T cells were already suppressed in response to anti-CD3 but still responded to anti-CD69 MAb. In these T cells, immobilized anti-CD3 failed to enhance simultaneous CD69 responses, although anti-CD3 enhanced CD69 responses in control T cells from uninfected donors. These results demonstrate an intrinsic defect in T-cell receptor-mediated T-cell activation, which could be a mechanism generating T-cell suppression during infection by T. cruzi.     

The specificity of suppressor T cells induced by chronic Mycobacterium avium infection in mice.

Normal mice infected intravenously with 10(6) or 10(8) viable M. avium develop persistent infections of the lungs, liver and spleen. The liver and spleen counts remained relatively constant whereas those for the lung slowly increased until eventually some of the animals began to die as a result of the infection. None of the heavily infected mice developed delayed hypersensitivity (DTH) to the M. avium cytoplasmic protein antigen (CPA). Spleen cells harvested at increasing time periods after the M. avium infection were tested for their blastogenic responsiveness to PHA and M. avium CPA. The presence of suppressor T cells within the heavily infected spleens was demonstrated by means of cell-mixing experiments before and after treatment of the anergic spleen cells with anti-Thy-1.2 antiserum and complement. The specificity of the suppressor T cells was measured in terms of their ability to depress responsiveness to sheep erythrocytes and an allograft challenge. Initially, the suppressor T cell population affected all of the T cell-mediated responses but as the infection progressed, so the non-specific host responses tended to return gradually towards normal, whereas the specific M. avium CPA-mediated suppression persisted largely unchanged.     

Protein malnutrition alters the distribution of Fc gamma R+ (T gamma) and Fc mu R+ (T mu) T lymphocytes in experimental pulmonary tuberculosis.

Inbred, strain 2 guinea pigs were given isocaloric diets containing either 30% (control diet) or 10% (low-protein diet) ovalbumin and infected 4 weeks later by the respiratory route with virulent Mycobacterium tuberculosis. By using an Fc receptor rosette assay, the proportions of T lymphocytes bearing Fc receptors for immunoglobulin G (T gamma cells) or immunoglobulin M (T mu cells) were quantified in blood and lymphoid tissues taken postinfection. A significant elevation in the proportion of the putative suppressor T subset (T gamma) in the blood of protein-deprived guinea pigs was observed at all intervals postinfection. Conversely, the levels of the putative helper T subset (T mu) in the bronchotracheal lymph nodes draining the site of virulent infection in malnourished animals were significantly reduced. Diet did not influence T gamma or T mu cells in the spleens. Diet-induced loss of purified protein derivative-specific T-cell functions in tuberculosis may be associated with alterations in the proportions of or the balances between T gamma and T mu subsets.     

Generation of anti-NZB red blood cell antibody-forming plasma cells from bone marrow cultures of syngeneic and allogeneic mice: functional modulation of helper T-cell subsets in autosensitization.

An in vitro anti-NZB red blood cell (RBC) autoantibody-forming system was developed by culturing young (antiglobulin negative) or old (antiglobulin positive) NZB mouse bone marrow cells in the presence of young or old NZB thymocyte homogenates (or RNA thymus extracts) and young NZB-RBC. Using young NZB bone marrow cells, the greatest number of autoantibody forming cells were seen following stimulation with a mixture of young and old thymocyte homogenates (TH). A higher response was seen with old NZB bone marrow cells stimulated by old NZB thymocyte homogenates and RBC. Phenol-extracted thymic RNA retained activity when added to bone marrow culture containing NZB-RBC. Thymus RNA from 9 to 10 days old NZB mice had no activity although their bone marrow cells responded well to stimulation by young and old thymic RNA together with RBC. By analysing results obtained using T-cells enriched for helper and suppressor activities, we have concluded that abrogation of self-tolerance in mice is due to the appearance of functionally modulated helper T-cell subsets and to imbalance between helper and suppressor T cells.     

Control of the Bcg gene of early resistance in mice to infections with BCG substrains and atypical mycobacteria.

The effect of the Bcg gene on the early host response to intravenous infection with a variety of BCG substrains and some atypical mycobacteria was investigated. The numbers of live bacilli of BCG Pasteur and BCG Tice recovered from the spleens of Bcgs mice (C57BL/6, B10.A and BALB/c) at 3 weeks following infection exceeded the bacterial dose injected, whereas the number of CFU recovered from the spleens of Bcgr mice (A/J, DBA/2 and C3H/HeN) did not exceed the number of CFU injected, thus following the pattern observed in Bcgr mice and Bcgs infected with BCG Montreal. BCG Russia failed to multiply in both test groups; however, the number of CFU recovered in Bcgr mice was significantly lower than in Bcgs mice. On the other hand, the presence of live bacilli in the spleens of either Bcgr or Bcgs mice injected with BCG Japan was undetectable in most cases. Involvement of the Bcg gene in the early resistance to infection with BCG Pasteur, BCG Russia, Mycobacterium kansasii and M. intracellulare was documented by the significant differences in the kinetics of infections in mice of the C.D2 (BALB/c-Bcgr) and BALB/c (Bcgs) congenic lines. In BCG Russia, M. intracellulare and M. fortuitum infections, the phenotypic expression of the Bcg gene resulted in a more rapid elimination of the bacteria in the spleens of Bcgr when compared with Bcgs mice. On the other hand, the hepatic granuloma formation correlated with bacterial load except when C.D2 mice were infected with a small dose of BCG Pasteur or M. kansasii where extensive granulomatous hepatitis developed although no bacterial multiplication occurred in the spleen. It is suggested that granuloma formation could depend of the properties of the mycobacteria as well as the genetic background of the host without implicating the bacterial burden.