Active suppression of host-versus-graft reaction in pregnant mice. VIII. The uterine decidua-associated suppressor cell is distinct from decidual NK cells

The fetus resulting from allogeneic mating expresses a variety of antigens that may serve as targets for rejection by the maternal immune system. Accumulation of non-T suppressor cells into the uterine decidua of allopregnant mice may serve to prevent such rejection. It has been previously shown that the suppressor activity in decidua during the second half of murine pregnancy is predominantly associated with a population of small lymphocytes with cytoplasmic granules that lack T-cell markers and inhibit the generation of cytotoxic lymphocytes (CTL) against paternal alloantigens both in vitro and in vivo. Since natural killer cells (NK) also possess cytoplasmic granules and may regulate the murine immune response, we examined the hypothesis that the decidua-associated non-T suppressor cell may represent a regulatory type of NK cell. Similar to NK cells, the decidua-associated suppressor cell expressed FcR for IgG. Unlike NK cells, the decidua-associated suppressor cell proved resistant to treatment with anti-asialo GM1 + C'. Sedimentation velocity examination demonstrated that decidua-associated NK activity was associated with cell population with a modal sedimentation of 4 mm/hr that was larger than the decidua-associated suppressor population. Potent suppressor cell activity was also recovered from the decidua of NK deficient allopregnant bg/bg mice. Therefore, decidua-associated NK cells and suppressor cells represent two distinct populations.

Indomethacin therapy abrogates the prostaglandin-mediated suppression of natural killer activity in tumor-bearing mice and prevents tumor metastasis

We have shown earlier that a decline in splenic natural killer (NK) activity during the development of transplanted or spontaneous tumors in mice results from an inactivation of NK lineage cells, mediated by prostaglandins (primarily PGE2) secreted by NK suppressor cells of the monocyte-macrophage lineage. In the present study we have used a C3H mouse mammary carcinoma model to examine whether this mechanism of NK suppression is conducive to tumor metastasis in vivo and whether a reversal of this suppression by a chronic indomethacin therapy can prevent metastatic spread from the primary tumor site. Three mammary tumor lines, all derived in our laboratory from a spontaneous C3H mammary tumor were employed: T-58 (uncloned parental line, having weak lung metastasizing ability from the subcutaneous site), C3 (a clone of T-58, showing high metastatic ability), and C10 (a nonmetastatic clone of T-58). Although the degree of NK susceptibility of these lines varied inversely with their metastatic potential, none was NK resistant. A chronic administration of indomethacin in the drinking water (14 micrograms/ml) to mice beginning on Day 4 after subcutaneous transplantation of 10(6) tumor cells resulted in a significant reduction in the growth rate of primary tumors in all hosts and led to a complete or nearly complete abrogation of lung metastasis in T-58- or C3-transplanted hosts examined at 1 month after tumor transplantation; C10-transplanted mice showed no metastasis in the control or the treated group. Concomitantly, there was a substantial restoration of splenic NK activity in all indomethacin-treated hosts. Plastic-adherent cells (greater than 95% macrophages) isolated from tumors growing in control mice, when coincubated for 20 hr with normal splenic effector cells caused a suppression of NK activity, reversible in the presence of indomethacin (10(-5) M) in vitro. Similar cells recovered from the residual primary tumors in indomethacin-treated mice had no suppressor ability. Chemically pure PGE2 (at concentrations of 0.5 to 1 X 10(-6) M, but not 0.25 X 10(-6) to 10(-8) M) also caused a suppression of NK activity of normal splenic effector cells, when added during the 4-hr 51Cr-release assay or allowed to interact with effector cells alone for a 20-hr incubation period; a removal of the cell-free PGE2 in the latter case prior to the NK assay did not relieve the suppression.(ABSTRACT TRUNCATED AT 400 WORDS)

Intrinsic B lymphocyte and macrophage defects in C3H/HeJ mice

C3H/HeJ mice are genetically defective in their responsiveness to lipopolysaccharide (LPS). Their B cells also have a characteristically low cloning efficiency in semisolid agar cultures, where LPS does not seem to be required. Adherent macrophages facilitate clonal proliferation in such cultures via diffusible substances. C3H/HeJ macrophages functioned poorly in this respect, and addition of normal C3HeB/FeJ macrophages to cultures of C3H/HeJ B cells did not lead to normal colony numbers. Although immune interferon can stimulate normal resident peritoneal macrophages to function well in semisolid agar cultures, it did not improve the cloning efficiency of C3H/HeJ cells. Similarly, addition of indomethacin or interleukin 1 to the cultures did not reveal that abnormally elevated production of prostaglandins or a deficiency in interleukin 1 are responsible for poor C3H/HeJ colony formation. These results indicate that C3H/HeJ mice have defects intrinsic to both B cells and macrophages that are not overcome by interferon. Purified B cells from these mice cloned poorly and did not respond to stimulation in liquid cultures with anti-mu-coated beads plus factors. There was a tendency for the poor cloning of C3H/HeJ B cells to improve with age.

In vivo mechanisms of alloreactivity. II. Allospecificity of cytotoxic T lymphocytes in sponge matrix allografts as determined by limiting dilution analysis

We have examined the frequency and alloantigen specificity of CTL that accumulate in sponge allografts (sponges seeded with allogeneic splenocytes) in sponge isografts (sponges seeded with syngeneic splenocytes), and in splenocyte-free sponge implants. Using limiting dilution analysis (LDA), we observed that sponge isografts and splenocyte-free sponge implants from C57BL/6 (H-2b) mice usually acquire small numbers of CTL (less than 250 cells per graft) with DBA/2 (H-2d)-reactivity or C3H/HeJ (H-2k)-reactivity. These alloreactive CTL are not detectable in conventional 51Cr-release assays, presumably because they are too infrequent and/or because they are inactive CTL precursors. When we examined the accumulation of alloreactive CTL in sponge allografts, we observed that DBA/2 sponge allografts from C57BL/6 recipients accumulate 10 to 100 times more DBA/2-reactive CTL than alloantigen-free sponge grafts. Nonetheless, these donor-reactive CTL rarely constitute more than 0.5% of the T cells recovered from sponge allografts, even at the peak of the rejection response. This raises questions concerning the remaining 99.5% of the allograft-infiltrating T cells. We were unable to detect by LDA any host-reactive CTL in sponge allografts, thus excluding the possibility that some of the remaining T cells were host-reactive CTL of donor origin which diluted graft-reactive T cells. However, using LDA we did detect a significant number of third-party (C3H/HeJ)-reactive CTL in sponge allografts, suggesting that the intense immune response at a graft site might facilitate indiscriminate recruitment of T lymphocytes. Alternatively, this enhanced third-party alloreactivity might reflect the proliferation of donor-reactive CTL with incidental crossreactivity for C3H/HeJ alloantigens. While testing these two alternatives, we observed that LDA cultures designed to detect third-party-reactive CTL could also support the growth of the in vivo-activated, donor-reactive CTL from sponge allografts; This compromised enumeration by LDA of the less frequent, third-party-reactive CTL by LDA. Although LDA is the only method that detects the growing population of third-party-reactive CTL in sponge allografts, technical restraints exclude LDA as a method of determining whether donor-reactive CTL and third-party-reactive CTL are separate or overlapping CTL subpopulations. Hence, it remains unclear if third-party-reactive CTL are a significant or insignificant proportion of the CTL that infiltrate sponge allografts.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytokine production and utilization by the motheaten mouse

Splenocytes from the motheaten mouse, after stimulation with alloantigen, lack the ability to utilize exogenous interleukin 1 (IL 1) or interleukin 2 (IL 2), express receptors for IL 2, or produce (IL 2). However, in contrast to other models of autoimmunity and immunodeficiency, after mitogen stimulation, motheaten splenocytes produced as much IL 1 or IL 2 as their normal littermates. In addition, these splenocytes expressed functional IL 2 receptors in the same quantity as normal littermate or wild-type splenocytes. Furthermore, motheaten thymocytes and splenocytes, like their normal littermates, respond synergistically to IL 1 on co-stimulation with mitogen, suggesting expression of an IL 1 receptor. Thus, motheaten mouse splenocytes are unable to utilize an antigen-delivered signal and convert it into cytokine production or IL 2 receptor expression. If the antigen signal is bypassed with mitogen, cytokine production and receptor expression appear normal.

Requirement of endogenous interferon-gamma production for resolution of Listeria monocytogenes infection

Peritoneal exudate cells and splenic cells of mice infected with Listeria monocytogenes show increased production of interferon-gamma (IFN-gamma) after antigen or mitogen stimulation. When an IFN-gamma-specific enzyme-linked immunosorbent assay was used, increased production was first observed 2 days after infection in peritoneal cells and 4 to 6 days after infection in splenic cells. The increased production of IFN-gamma correlated with the clearance of Listeria from the peritoneal cavity and spleen. Macrophages derived from mice at these times were activated as evidenced by expression of nonspecific tumoricidal activity against 111In-labeled P815 mastocytoma cells. Injection of neutralizing monoclonal anti-IFN-gamma into 1-day-infected mice completely inhibited the generation of activated macrophages. Normal hamster IgG had no effect. In vivo, the monoclonal antibody also abrogated clearance of bacteria from the spleen and peritoneal cavity. Six days after injection of a sublethal dose of Listeria, the peritoneal cavity of control mice treated with normal hamster IgG was devoid of bacteria and the spleen contained less than 10(3) colony-forming units. However, mice treated with anti-IFN-gamma carried more than 8 X 10(6) colony-forming units in either anatomical site at day 6 and exhibited a higher mortality rate. These results indicate that IFN-gamma production is required for the in vivo generation of activated macrophages and the clearance of bacteria during Listeria infection.

Comparison of immune responses between high and low responder strains of mice in the concomitant immunity and vaccine models of resistance to Schistosoma mansoni

Mice of the inbred P strain fail to develop significant resistance to challenge Schistosoma mansoni infection at 6 weeks after either low-grade primary infection or vaccination with attenuated homologous parasites, in contrast to other strains such as C57Bl/6, and thus provide a model for comparison of potential immune resistance mechanisms in low versus high responder animals. In this study, the antigen-specific cellular responses found to correlate with resistance in these strains were delayed cutaneous hypersensitivity, production of macrophage activating lymphokine and macrophage larvicidal activity, all of which were greater in infected or vaccinated C57Bl/6 mice than in similarly immunized but non-resistant P mice. Humoral responses correlating with resistance were IgM reactivity to schistosomula surface antigens in both infected and vaccinated animals, as well as both IgM and IgG reactivity to soluble schistosome antigens in infected mice. Immune responses that showed no relationship with resistance included IgG reactivity to larval surface antigens and immediate hypersensitivity to soluble worm antigens. In infected mice, neither granuloma size nor extent of hepatic fibrosis correlated positively with resistance to challenge infection. Thus, similarities exist between patterns of resistance and immune response at this early time after immunization with either viable or attenuated parasites. These observations suggest that common immune effector mechanisms could be involved, with activated macrophages playing a central role in resistance.

[Capacity for IgE antibody production in ASK mice]

The capacity for IgE anti body production in ASK mice, which are highly sensitivity to anaphylactic shock, was compared with that in C3H and AKR mice. Three strains of mice were immunized with DNP-Ascaris mixed with aluminum hydroxide gel. IgE antibody to DNP in the sera was titrated by the rat 48-hour passive cutaneous anaphylaxis test. Maximum IgE titers of each strain of mice were 1: 2560 in C3H, 1: 1280 in ASK and 1: 640 in AKR. IgE antibody was detected in the sera until 170 days in C3H, 290 days in ASK and for not less than 320 days in AKR. These results suggest that the ASK mouse is a high responder strain for IgE antibody.

Immunohistochemical detection of mammary tumor virus antigens in sweat and sebaceous glands of mice

Mammary tumor virus (MTV) antigens in both sexes of GRS/A, SHN and C3H mice were examined in the sweat and sebaceous glands by immunoperoxidase technique using antiserum against gp52, envelope protein, or p27, core protein. Balb/c mice were used for reciprocal foster nursing with these inbreds to discriminate the expression of endogenous MTV from that of exogenous MTV. Both antigens were first detected around the age of 4 months in the sweat glands of mice with endogenous GR- or SHN- MTV. A linear staining of gp52 was seen along the luminal borders of glandular cells, and the reaction products for gp52 were demonstrated on the apical cell membranes, where no virion could be seen ultrastructurally. A diffuse staining of p27 was found in the cytoplasm of some glandular cells, where MTV particles could not be detected. In the sebaceous gland of the same mice, however, only p27 was first detected at the age of 60 days. A dot-like staining of p27 was found in the perinuclear region of some glandular cells, where an aggregation of intracytoplasmic A particles could be seen under an electron microscope. These positive stainings were unrelated to sex. In such skin appendages of all examined C3H mice and Balb/c mice with GR- or SHN- MTV, no antigen expression could be seen up to the age of 500 days. Therefore, some genes might be able to regulate the expression of endogenous MTV antigens in the skin appendages, while their glandular cells would have no receptor for exogenous MTV, namely the so-called "milk factor".

Favorable influences of imuthiol on mouse reproduction and immune system of offspring

A physiological immature immune system in newborns is a common feature frequently associated with increased susceptibility to infections. The properties of imuthiol (purified sodium diethyldithiocarbamate), an agent specifically active on the T-cell lineage, and virtually devoid of toxicity for man or animals, encouraged us to determine whether imuthiol administered to the dams could increase the immune capability of offspring without altering fecundability and birth rate. Experiments performed either in histocompatible or histoincompatible mating systems, show that chronic administration of imuthiol prior to mating and/or during pregnancy stimulated newborn mice to increased T-cell-dependent responses, without altering birth rates and growth curves in progenies. The data suggest that imuthiol has no teratogenicity or deleterious influences on mouse gametes, and might be useful to prevent immunodepression-associated infections in newborns.

Evidence for separate genetic defects in C3H/HeJ and C3HeB/FeJ mice, that affect susceptibility to gram-negative infections

Past studies have suggested a linkage between susceptibility to Salmonella typhimurium infection and the Lpsd genotype in C3H mice. Recently, this linkage was questioned by the finding that C3HeB/FeJ mice (Lpsn,Lpsn) were highly susceptible to systemic S. typhimurium infection. The present study shows a marked difference between C3H/HeJ and C3HeB/FeJ in their susceptibility to Gram-negative urinary tract infection. The number of E. coli and S. typhimurium recovered from the kidneys 24 hr after infection was 70 to 100 times higher in C3H/HeJ than in C3HeB/FeJ or C3H/HeN mice. Subsequently, in C3HeB/FeJ mice S. typhimurium multiplied to the level of C3H/HeJ mice, resulting in a shorter mean survival time of C3H/HeJ and C3HeB/FeJ compared with C3H/HeN mice. In contrast, E. coli remained localized to the urinary tract of C3H/HeJ mice but were eliminated from C3HeB/FeJ and C3H/HeN mice. Thus, experimental E. coli urinary tract infection appears to provide a method to differentiate the genetic defects of C3H/HeJ and C3HeB/FeJ mice. The results support an influence of the Lpsd genotype on clearance of Gram-negative bacteria from the kidneys of C3H mice.

Generation and characterization of mouse monoclonal antibodies to the myelin-associated glycoprotein (MAG)

A panel of mouse monoclonal antibodies to rat and human myelin-associated glycoprotein (MAG) was developed. Normal mice were unresponsive to rat MAG, and successful immunization with rat MAG was only achieved in autoimmune NZB mice. By contrast, all strains of mice were responsive to human MAG. The monoclonal antibodies developed differ with respect to immunoglobulin type, their specificity for human and/or rat MAG, and their recognition of protein or carbohydrate epitopes in MAG. In general, the antibodies that react with the protein backbone recognize both rat and human MAG, whereas a large number of the monoclonal antibodies recognize a carbohydrate determinant in human MAG that is not in rat MAG. Immunocytochemical staining of adult human spinal cord with the monoclonal antibodies resulted in periaxonal staining of myelin sheaths similar to that produced by well-defined, rabbit, polyclonal anti-MAG serum. In addition, the antibodies recognizing carbohydrate determinants in human MAG strongly stained oligodendrocyte cytoplasm. These monoclonal antibodies will be of value for the further chemical and biological characterization of MAG.

Macrophage-mediated mitogenic suppression induced in mice of the C3H lineage by a vaccine strain of Salmonella typhimurium

Salmonella typhimurium, strain SL3235, an avirulent organism, has been used as a live vaccine in mice of the C3H lineage and has been found to confer high levels of protection. In the present study, it was found that intraperitoneal injection of approximately 5 X 10(5) live SL3235 induced potent suppression of spleen cell mitogenic responses to a panel of B- and T-cell mitogens in the Salmonella-hypersusceptible C3H/HeJ and C3HeB/FeJ, and the inherently resistant C3H/HeNCrlBR mice. Maximal suppression (greater than 99%) was seen at 1 week, and was still significant but waning (50%) at 3 weeks postimmunization. In contrast, cells of mice receiving acetone-killed cells were not suppressed. Removal of macrophages, but not T or B cells, restored responsiveness, indicating that suppression was macrophage mediated. Prostaglandins were not the major mediator of suppression, as in vitro administration of indomethacin failed to abrogate suppression. As mitogenic suppression occurred in mice with high levels of Salmonella immunity, the suppression is interpreted as a marker of a powerful immunomodulatory process induced by live cells, rather than as an indication of poor immune status of the host.

Modulation of in vitro natural cell-mediated activity against enteropathogenic bacteria by simple sugars

Lymphoid cells from mouse Peyer's patches and spleens were tested in a 2-h in vitro assay for their natural activity against the enteropathogenic bacteria Salmonella typhimurium, Salmonella enteritidis, Salmonella tel aviv, and Shigella sp. X16. The antibacterial activity expressed by normal cells was detected against all the bacterial strains tested with the exception of Peyer's patch lymphocytes against S. tel aviv and splenocytes against Shigella sp. X16. To determine whether the different expression of natural antibacterial activity might be due to lectin-like proteins interacting with the saccharidic moieties of the bacterial wall, 11 simple sugars were preincubated with the effector cells before the in vitro assays. We found that some of them could block the natural antibacterial activity as well as induce antibacterial activity when this was not spontaneously expressed. Interestingly, a different panel of sugars among those employed was observed to affect the antibacterial activities for each of the above-mentioned bacterial targets and each effector cell. However, the same panel of sugars was able to block or stimulate the lymphocyte activity when bacteria with the same somatic antigens as two substrains of S. typhimurium and one strain of Salmonella schottmuelleri were employed. To further investigate the interaction between effector cells and bacteria, effector cells or Shigella sp. X16 targets were treated with proteolytic, glycolytic, and lipolytic enzymes before the in vitro assays. Furthermore, EDTA was used to analyze the role of divalent cations in this experimental system. The results obtained suggest that lectin-like proteins playing a role in this interaction are present not only on lymphocytes but also on bacteria and that divalent cations are essential for the expression of in vitro antibacterial activity.

Strain dependence of muramyl dipeptide-induced LAF(IL 1) release by murine-adherent peritoneal cells

The capacity of MDP to stimulate LAF(IL 1) production by adherent peritoneal cells (APC) from different strains of mice was examined. It was observed that MDP could stimulate thioglycollate-induced APC from DBA/2, C57B1/6, and CBA/CA mice, but not from C3H mice. Resident APC from DBA/2 or C3H/HeJ mice were also responders and nonresponders, respectively, to MDP for LAF(IL 1) production, the positive effect of MDP being more marked on DBA/2 cells in the presence of indomethacin. Because a LPS high-responder C3H substrain (C3HeB/Fe) did not respond to MDP, it was concluded that the strain dependence with respect to the induction of LAF(IL 1) seen with both MDP and LPS was not linked. Moreover, the unresponsiveness of C3H mice to MDP was not linked to their MHC haplotype, because a second H-2k strain (CBA/CA) was a good responder to MDP stimulation.

Difference in susceptibility to gram-negative urinary tract infection between C3H/HeJ and C3H/HeN mice

The difference in susceptibility to urinary tract infection between C3H/HeJ and C3H/HeN mice was tested for with gram-negative strains differing in lipopolysaccharide composition. Recently, impaired clearance of Escherichia coli from the kidney of C3H/HeJ compared to C3H/HeN mice was shown to be correlated with the LPS low responsiveness. In this study, a difference in clearance from the kidneys of C3H/HeJ and C3H/HeN mice was found only with lipopolysaccharide-containing bacteria. Gram-positive bacteria, e.g., Staphylococcus saprophyticus and Streptococcus agalactiae, were recovered in essentially equal numbers from the kidneys of mice of both strains. In contrast, of the lipopolysaccharide-containing strains used, all persisted in higher numbers in the kidneys of C3H/HeJ mice than in the kidneys of C3H/HeN mice. Variations in the O side chain did not eliminate this difference. E. coli Hu734 O75+K5+ and the rfb- mutant O75-K5+ remained in similar numbers in C3H/HeJ mice, although O75-K5+ was eliminated more rapidly in C3H/HeN mice. The core structure did not affect the differential persistence in the two mouse strains. The rfb mutants with R1-R4 cores were eliminated after 24 h from the C3H/HeN mice, but remained in significant numbers in the kidneys of C3H/HeJ mice. Even the Re mutant of Salmonella minnesota persisted in low numbers in C3H/HeJ mice. The relative bacterial recovery from either mouse strain was related to the overall virulence of the infecting bacterial strain, but the difference between C3H/HeJ and C3H/HeN mice was associated with responsiveness to parts of lipopolysaccharide common to the bacterial strains tested.

Differences in delayed-type hypersensitivity responses in various mouse strains in the C3H lineage infected with Salmonella typhimurium, strain SL3235

Immunization with a virulent Salmonella typhimurium, strain SL3235, has been found to provide high levels of protection against challenge with virulent Salmonella in hypersusceptible mouse strains in the C3H lineage. These mouse strains include the lipopolysaccharide-hyporesponsive C3/HeJ mouse and the closely related but lipopolysaccharide-responsive C3HeB/FeJ mouse. To assess the role of cellular immunity in the protection elicited by this attentuated organism, delayed-type hypersensitivity (DTH) was measured in these mouse strains and in inherently resistant mice. Of the mouse strains tested, only the inherently resistant CD-1 and C3H/HeNCrlBR mice developed significant DTH responses, as assessed by footpad swelling tested at various times after immunization with SL3235. The hypersusceptible C3H/HeJ and C3HeB/FeJ mice failed to exhibit significant DTH responses despite their high levels of immunity.

Delayed-type hypersensitivity after immunization with ultrasonicated Mycobacterium lepraemurium in C3H and C57BL mice

Subcutaneous immunization with ultrasonicated Mycobacterium lepraemurium (MLMSon) in incomplete Freund's adjuvant (IFA) induced long-lasting skin reactivity with the kinetics of a tuberculin-type delayed hypersensitivity (DTH) reaction in both C3H and C57BL mice. The reactivity generally was stronger in C57BL than in C3H mice, and with increasing doses of MLMSon test antigen the local reaction increased more in C57BL than in C3H mice. Pretreatment of C3H mice with cyclophosphamide before immunization caused a shift in the dose-response curve so that the local reaction increased more with increasing doses of test antigen. Histological examination of the reaction elicited by MLMSon in immunized mice revealed a predominantly mononuclear cell infiltrate, and local reactivity could be transferred by immune cells but not by immune serum. The local reaction elicited by MLMSon exerted an adjuvant effect on the induction of DTH to sheep erythrocytes. Thus, MLMSon in IFA given subcutaneously induced stable DTH that conformed to the criteria for tuberculin-type DTH.

[Effect of exogenous RNA preparations on the antitumor activity of the splenocytes in C3HA mice]

Tumor growth inhibition was compared in animals implanted a mixture of tumor cells and splenocytes, treated or non-treated with RNA preparations. The latter were isolated from the spleens of C3ha mice, both intact (control--cRNA) and immunized with normal tissues of syngeneic or allogeneic animals (immune--imRNA). Examination of various samples of splencytes of intact C3HA mice show that treatment with cRNA and imRNA preparations changes occasionally their antitumor activity in relation to MGXXIIa hepatoma cells. In the majority of the experiments effects of cRNA and imRNA on splenocytes were unidirectional. Molecular and cellular mechanisms of this phenomenon are discussed.

Tail lesions in C3H/He mice

C3H/He mice obtained from different suppliers developed tail lesions shortly after arrival. Histologically no inclusion bodies could be shown. A serological survey of diseased mice was negative for those viruses which may cause skin lesions. The disease could not be transmitted to healthy mice and no virus could be cultured from the skin lesions. It is concluded that the syndrome was induced by stress, in this case transport from the United Kingdom to the Netherlands.

Trypanosoma rhodesiense: analysis of the genetic control of resistance among mice

Inbred mouse strains differ in their resistance to infection with the human pathogen Trypanosoma rhodesiense. Of the strains tested, C57BL/6 (B6) mice were the most resistant, and BALB/c (C) mice were among the most susceptible. The genetic basis underlying the different susceptibility of these two strains was analyzed. (CXB6)F1 progeny of either sex were more resistant than the BALB/c parent. Also, the backcross of F1 mice to the susceptible male or female BALB/c parent resulted in 52.0% susceptible (i.e., death on or before day 24) progeny, as compared with only 0.64% susceptible F1 progeny. The data suggested that resistance was the dominant phenotype and that the resistant allele was carried by the B6 parent. The presence of another locus regulating resistance to death was suggested by the facts that only a small percentage of F2 mice were susceptible and that a number of F1 and F2 mice were more resistant than their B6 parent. The locus responsible for these phenomena was presumably hypostatic in nature and carried by BALB/c mice, and its effects were only evident in the presence of other resistance genes. In addition, the observation that many of the susceptible individuals among F2 and backcross mice were more resistant than the BALB/c mice suggested that other minor genes also modulated the response of mice to infection. A set of CXB recombinant inbred mice was tested as well, and the individual strains within this set could also be placed into four groups: susceptible, intermediate, resistant, or hyperresistant. These findings are compatible with the multigenic model suggested by the Mendelian analyses.

BCG-induced anaemia in mice: no direct effect of the growth of bacilli

Mice receiving viable BCG intravenously (i. v.) rapidly and transiently develop anaemia, the origin of which is a decrease in erythropoietic progenitor cells. BCG-induced anaemia appears to be related to conditions which allow the development of a protective immune response against BCG infection. An increased number of blood phagocytes is strictly associated with the development of the anaemia and is dependent on the presence of T lymphocytes. Anaemia does not occur in some strains of mice: C3H/He Past strain was chosen as a typical non-responding strain and the opposite C57BL/6 strain as a responding one. Enumerations of BCG particles were performed in haemopoietic tissues, spleen and bone marrow of mice of the two strains in order to appreciate an eventual direct effect of bacilli growth on erythropoiesis. We never observed the particular growth of bacilli in mice which developed anaemia. On the contrary, the number of BCG viable units decreased progressively in responding strain C57BL/6 when numerations were performed after the 2nd month of the infection. This ability of C57BL/6 mice to control the infection contrasted with a relapse of bacilli growth in C3H.