Cell-to-cell interaction in the immune response. IX. Regulation of hepten-specific antibody class by carrier priming.

Mice primed to horse erythrocytes (HRBC) produced greatly enhanced 3,5-dinitro,4-hydroxyphenylacetic (NNP)-specific indirect plaque-forming cell (7S PFC) responses when given NNP.HRBC but no difference in hapten-specific direct (19S PFC) responses in comparison to non-carrier-primed mice. The effect was carrier specific and could not be produced by simultaneous challenge of rabbit erythrocyte (RRBC)-primed mice with RRBC and NNP.HRBC. When spleen cells from HRBC-primed mice were transferred to irradiated recipients, there was again an enhanced 7S response to NNP.HRBC. The primed spleen cells could be replaced by giving activated thymus cells to HRBC together with normal spleen as a source of B cells. It is concluded that T cells influence not only the amount but also the class of antibody formed by hapten-sensitive B cells.

Cell-to-cell interaction in the immune response. X. T-cell-dependent suppression in tolerant mice.

Specific immunological tolerance was induced in CBA mice by a single injection of deaggregated fowl immunoglobulin G (FgammaG). The unresponsive state was stable on adoptive transfer and irreversible by pretreatment of tolerant cells with trypsin. Tolerant spleen cells could suppress the response of normal syngeneic recipients. They also suppressed the adoptive primary response of spleen cells to FgammaG in irradiated hosts. The inhibitory effect was on the indirect (7S) plaque-forming cell (PFC) response. Incubation of the tolerant cell population with anti-theta serum and complement reversed the suppressor effect. Furthermore, the addition of purified T cells from normal donors restored the capacity of the anti-theta serum-treated tolerant cells to transfer an adoptive response to FgammaG. The existence of FgammaG-reactive B cells was supported by the demonstration of normal numbers of antigen-binding cells in the spleen and thoracic duct lymph from tolerant animals. Moreover, the formation of caps by these cells implied that they could bind antigen normally. These experiments provided direct evidence for the existence of suppressor T cells in the tolerant population. Further evidence was derived from examination of the effect of antigen "suicide". Tolerant spleen cells were treated with radioactive FgammaG under conditions known to abrogate T-cell helper function. When these cells were transferred together with normal spleen cells into irradiated hosts, suppression of the primary adoptive response to FgammaG was no longer observed. Inhibition of an adoptive secondary response to FgammaG was obtained by transferring tolerant spleen cells with primed B cells provided high doses of tolerant cells were used. By contrast low doses exerted a helper rather than a suppressor effect in this system.

How do macrophages distinguish the living from the dead?

Injection of live but not dead bacteria induces a wave of IL-12 and subsequently, IFN-gamma production. Surprisingly, in vitro, both live and dead bacteria elicit IL-12 from macrophages. Better understanding of how macrophages distinguish live from dead bacteria would help explain this difference and possibly bypass the need for live vaccines against intracellular bacteria.

Functional deficiencies of peritoneal cells from gene-targeted mice lacking G-CSF or GM-CSF.

Gene-targeted mice lacking the hemopoietic growth factors, granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage (GM)-CSF, show increased susceptibility to infection with the facultative intracellular bacterium, Listeria monocytogenes. The resident peritoneal cell populations from G-CSF(-/-) and GM-CSF(-/-) mice showed reduced production of the bactericidal molecule nitric oxide. Macrophage-mediated tumoricidal activity and phagocytosis of Listeria were reduced in G-CSF(-/-), but not in GM-CSF(-/-), mice. In G-CSF(-/-) mice, there was an unexpected expansion (from 18% in WT to 38%) of a population of cells with morphology intermediate between typical macrophages and typical lymphocytes. These cells had some of the features of poorly differentiated macrophages, being adherent to plastic but poorly phagocytic, nonspecific esterase positive but myeloperoxidase negative. They were largely negative for the macrophage marker F4/80 and for Thy1, B220, and Gr1. Their disproportionate presence, and the corresponding deficiency in typical macrophages, possibly accounts for some of the functional deficiencies observed in G-CSF(-/-) mice.

Pathogenesis and cellular immunity in experimental murine brucellosis.

Infection of mice with Brucella abortus strain 19 provides a most useful and interesting model in which to study chronic infection with intracellular bacteria. Most strains of mice develop a chronic infection. However, certain strains are better able to handle their infection. Long term bone marrow chimeras showed this to be due to bone marrow derived cells, rather than host physiology, although whether it is due T or B lymphocytes, macrophages or polymorphs is yet to be determined. In vitro treatment of lymphocytes from infected donors showed that the subpopulations transferring protection to naive mice was Thy 1+ 2+ Ia-. i.e. the same T cell which induces cell mediated immunity to Listeria. In vivo injection of an optimal regime of anti Ly1 monoclonal antibody exacerbated infection and removed the population of cells transferring immunity. Sub-optimal amounts of anti-Ly-1 abrogated IgG Brucella agglutinating antibody without affecting bacterial numbers, thus confirming the T dependence of IgG antibody and suggesting that it is not important in recovery from infection. Marked splenomegaly occurred about 3 weeks after infection of the mice. It was transferred by T lymphocytes and involved marked influx of macrophages, increased haemopoiesis, fibrin deposition and fluid in the spleen. Although the macrophages were immunosuppressive in vitro they did not appear to account for chronicity of infection. In seeking to account for this chronicity we have compared a number of aspects of the immune response in chronically infected mice and in mice which were able to control their infection. Although we have ruled out a number of possibilities, we have not yet established the basis of chronicity.

The cellular source of interleukin-6 during Listeria infection.

The cellular source of interleukin-6 (IL-6) during infection of mice with Listeria monocytogenes was investigated both in vitro and in vivo. Peritoneal cells taken at intervals from infected mice and cultured in vitro without added stimulus produced high titers of IL-6 peaking 2 days postinfection in a time course similar to that observed in vivo. Adherent cells with the morphology of macrophages were a major source of this IL-6. Spleen cells similarly harvested at intervals and cultured with heat-killed Listeria or heat-killed Brucella organisms as specific and nonspecific stimuli, respectively, showed two distinct IL-6 responses: (i) an early-phase response up to 5 days after infection when IL-6 production was elicited by either a specific or nonspecific stimulus, and when depletion of T cells had no effect, and (ii) a later response 7 to 10 days after infection when very high levels of IL-6 were produced in response to a specific stimulus. This response was lost when T cells were depleted in vitro or in vivo or in spleen cell cultures from mice with severe combined immunodeficiency. However, studies in vivo failed to show an important role for T cells governing serum IL-6. We conclude that most of IL-6 detected in vivo is produced by nonlymphocytes. Whether IL-6 produced by T lymphocytes in local foci of infection has any role in resolution of that infection is unknown.

Listeriosis in beige mice and their heterozygous littermates.

The ability to resist the facultative intracellular bacterium Listeria monocytogenes was not impaired in the beige mutants of C57BL/6J mice which are known to be deficient in a number of immune functions. The intravenous LD50 of Listeria in beige (bg/bg) mice and their normal heterozygous (bg +) littermates was approximately 5 X 10(5). Growth of Listeria in the spleen and liver during primary and secondary infections was similar in the two groups of mice, and each was able to act efficiently in adoptive transfer of immunity. Histological examination showed a normal accumulation of polymorphonuclear and mononuclear cells at foci of infection in the liver, while in the spleen the previously described depletion of T cells 2-4 days after infection was observed in both groups. In-vitro 18-hr cytotoxicity of peritoneal cells for P815 targets, a function usually attributed to macrophages, was increased 2 days after infection in both bg/bg and bg/+ mice. In contrast, 4 hr cytotoxicity of spleen cells for YAC-1 targets, considered typical of natural killer (NK) cells, was depressed in uninfected bg/bg mice and only slightly raised during infection. This compared with a normal NK activity in uninfected bg/+ mice which was markedly increased during infection.

Non-major histocompatibility complex control of antibody isotype and Th1 versus Th2 cytokines during experimental infection of mice with Mycobacterium avium.

Infection of different strains of mice with Mycobacterium avium has revealed genetic control of the immunoglobulin isotype induced and of the balance between Th1 and Th2 cytokines. Female BALB/c or C57BL/10 mice were infected intranasally with 10(5) M. avium organisms. The antibody response was measured over 18 weeks by enzyme-linked immunosorbent assay and Western blotting, while numbers of cytokine-producing cells were assessed at 12 to 15 weeks by ELISPOT assay. Upon infection, C57BL/10 mice produced a clear Th1 response with strong gamma interferon (IFN-gamma) production, no interleukin-4 (IL-4), and almost entirely immunoglobulin G2a (IgG2a) antibody. In contrast, BALB/c mice developed T cells producing IL-4, as well as those producing IFN-gamma, while the antibody response was a mixture of IgG1 and IgG2a. Antibodies from BALB/c mice were also able to recognize a greater range of antigens than were C56BL/10 mice. B10D2 mice, which carry the BALB/c major histocompatibility complex haplotype on a C57BL/10 background, followed the C57BL/10 cytokine pattern. Mice infected with Listeria monocytogenes did not show a similar response dichotomy.

Activated macrophages in congenitally athymic "nude mice" and in lethally irradiate mice.

Resistance to the facultative intracellular bacteria, Brucella abortus and Listeria monocytogenes, is principally the result of acquisition of enhanced antibacterial activity by host macrophages, probably in response to lymphokines released by T lymphocytes. However, the present paper describes a surprisingly high resistance on the part of both congenitally athymic "nude" mice and of lethally irradiated mice compared with normal controls. This enhanced bactericidal activity was evident 24 hr after infection, and could also be demonstrated in macrophages from nude mice cultured in vitro. It was concluded that the macrophages of these animals had been activated before infection.

Haemopoiesis in mice genetically lacking granulocyte-macrophage colony stimulating factor during chronic infection with Mycobacterium avium.

In order to test the role of granulocyte-macrophage colony stimulating factor (GM-CSF) in haemopoiesis during chronic infection, mice with a targeted disruption of the gene for GM-CSF were infected intraperitoneally with the facultative intracellular pathogen, Mycobacterium avium. The bacteria spread to lungs, liver and spleen and persisted for more than 10 weeks at levels between 105 and 106 CFU. Bacterial numbers did not differ significantly between infected GM-CSF-/- and wild-type mice, making this an excellent model in which to study the effects of GM-CSF deficiency on haemopoietic cells without complications of interpretation relating to differences in bacterial load. Haemopoietic colony forming cells (CFC) in the bone marrow of GM-CSF-/- mice before infection were not different from wild-type. However, whereas CFC in wild-type mice increased 1.5-fold with infection, GM-CSF-/- mice were unable to increase their CFC and numbers were significantly lower than in infected wild-type mice. Cells attracted to the peritoneal cavity of the GM-CSF-/- mice following i.p. injection of bacteria were notably lacking in the large, granular macrophages of activated appearance, which were a feature in wild-type mice. Nitric oxide production by peritoneal cells from GM-CSF-/- mice was deficient. Thus, GM-CSF is not critical for haemopoiesis during chronic infection, but in its absence the mice are unable to increase their output of haemopoietic cells and there are deficiencies in macrophage activation.

Endogenous gamma interferon mediates resistance to Brucella abortus infection.

Depletion of endogenous gamma interferon (IFN-gamma) with anti-IFN-gamma monoclonal antibody resulted in increased numbers of Brucella abortus in the spleen and liver of infected CBA mice. This increase was accompanied by a decrease in splenomegaly and a lower proportion of macrophages in the spleen. Furthermore, treatment of recipient mice with anti-IFN-gamma antibody blocked the adoptive transfer of resistance with immune T cells. Together, the results indicated that endogenous IFN-gamma plays an important role in mediating resistance to primary and secondary Brucella infection.

Macrophage activation during experimental murine brucellosis: a basis for chronic infection.

Evidence is presented that the chronicity of infection in CBA mice after injection of Brucella abortus 19 is related to a number of factors: (i) the relative resistance of B. abortus to macrophage killing, which allowed some bacteria to survive the peak of macrophage activity occurring at 14 days; (ii) the decline in macrophage activity thereafter (this decline was related in part to the presence of fewer bacteria to stimulate the bactericidal activity and also to specific, active suppressor mechanisms not identified in this study); and (iii) the insensitivity of the persistent Brucella organisms to activated macrophages. This was not due to a selection of genetically resistant bacteria, but possibly to their inaccessibility, either within "incompetent" macrophages or outside macrophages altogether.

Activation of non-specific cytotoxic cells in Listeria-susceptible and -resistant mouse strains.

An increase in macrophage tumouricidal activity in the spleen was demonstrated following intravenous infection of genetically resistant C57BL/10 mice with Listeria monocytogenes, but not after infection of BALB/c mice. However, tumouricidal macrophages appeared in the peritoneal cavity of both strains after infection, while NK cell activity was generally higher in BALB/c mice. The activation of tumouricidal macrophages and NK cells in the C57BL/B10 mice was T independent and, at least in the peritoneal cavity, radioresistant (600 rads). The relevance of these results to the genetic control of resistance to Listeria is discussed.

Relationship between colony-stimulating activity and interferon production during infection.

Normal mouse spleen, when cultured in vitro for 3 days in the presence of 10(8) heat-killed Listeria monocytogenes organisms, produced colony-stimulating factors (CSF) that were capable of supporting the production of haemopoietic colonies by bone marrow cells in semi-solid agar, or supporting bone marrow proliferation in liquid medium. In contrast, when the spleen cells were prepared from mice that had been infected with Listeria monocytogenes, colony-stimulating activity (CSA) was no longer detectable over a period from Day 3 to Day 17 post-infection. Suppression of CSA was imposed on normal spleen cells when nylon-wool filtered, T-cell enriched spleen cells from infected mice were co-cultured with normal spleen cells. Suppression largely coincided with the production of interferon by whole spleen from infected mice, and when interferon-gamma (IFN-gamma) was neutralized by antibody CSA was again detected. An early IFN-gamma-independent decrease in CSA production was also detected 2-3 days post-infection. The relevance of this system to the control of CSF production in vivo is discussed.

Either B7-1 or B7-2 is required for Listeria monocytogenes-specific production of gamma interferon and interleukin-2.

Listeria infection results in the induction of gamma interferon (IFN-gamma)-producing T lymphocytes. Blocking of the costimulatory molecule B7 in vivo led to a marked decrease in antigen-specific production of IFN-gamma and interleukin-2 by lymphocytes. Blocking of both B7-1 (CD80) and B7-2 (CD86) was required in order to inhibit cytokine production, indicating that either molecule could act alone. Although IFN-gamma production by cultured spleen cells was significantly suppressed by B7 blocking, mice cleared primary and secondary Listeria infection as effectively as control mice.