Site of action of serum factors that block delayed-type hypersensitivity in mice

Production of dengue virus-induced macrophage cytotoxin in vivo

We have observed that dengue virus-induced cytotoxic factor (CF) induces peritoneal and splenic macrophages in vitro to produce a cytotoxin (CF2). This study demonstrates also production of CF2 in vivo in DV-infected mice and following inoculation with CF. The cell-type responsible for CF2 production in vivo is the macrophage (M phi) as M phi-depleted mice failed to produce CF2. CF2 activity could not be observed in the serum or peritoneal fluid though it is produced in peritoneal M phi. Once stimulated, CF2 is present for 4 h in M phi. M phi can be restimulated to produce CF2 only after a refractory period of 48 h.

Modification of immune induction by adjuvant

The role of adjuvanticity in the modification of the immune induction was studied by separate application of antigen and adjuvant in mice. An antigen specific plaque forming cell (PFC) test and a delayed type hypersensitivity (DTH) assay were used for these studies. Antigen (SRBC) and adjuvant were applied separately in time and place. A stable well defined water-in-oil emulsion without antigen was used as adjuvant. Our studies have shown that intraperitoneal (i.p.) injection of this adjuvant stimulates the intravenous (i.v.) induced PFC response, while the DTH response is suppressed. This effect can be demonstrated even when adjuvant has been injected i.p. 5 days prior to i.v. antigen injection. The stimulation of the PFC response depends on the dosage of i.v. injected antigen.

Immunogenicity of antigen complexed with antibody. I. Role of different isotypes

IgM-, IgG1-, IgG2a-, IgG2b- and IgE-type anti-ovalbumin antibodies were isolated from rat immune sera and the complexes formed by antibodies of a defined isotype and the antigen were compared for antibody avidity and interaction with homologous complement. IgG2a-containing complexes consumed total complement with the greatest efficiency. IgG2a-, IgG2b- and IgM-containing complexes displayed similar activities in activation of the alternative pathway while IgG1 was less efficient. Reduction and alkylation of IgG2a antibodies abolished the capacity of the complex to activate the alternative pathway, but not their total complement consumption. The complement-dependent solubilization was greatest when complexes contained IgG1- or IgM-type antibodies and lowest with IgG2a-containing complexes. Inbred Long Evans rats immunized by complexes containing IgG1 or IgG2b antibodies displayed a markedly lower delayed-type hypersensitivity (DTH) compared with those immunized by antigen alone. Immunization with IgG2a- or IgE-containing complexes resulted in a slightly decreased DTH, while IgM-containing complexes induced DTH like ovalbumin alone. IgG2a-containing complexes elicited an antibody response markedly higher than that found in animals immunized by antigen alone. The same effect was found when complexes contained reduced-alkylated IgG2a. Immunization with complexes containing the other isotypes involved in the study induced an antibody response similar to the antigen in phosphate-buffered saline.

Mechanisms in the in vivo release of lymphokines: relationship of high and low responsiveness to other parameters of the immune response

Variations exist between different strains of inbred mice in the release of lymphokines into the circulation. A number of manifestations of cell-mediated immunity in mice sensitized intravenously with Mycobacterium bovis BCG were analyzed to determine their association with the in vivo release of gamma interferon (IFN-gamma) and migration inhibitory factor. Differences occurred among the strains in the proliferative responses of splenic cells to specific antigen and in the release of IFN after the challenge of BCG-sensitized mice with lipopolysaccharide. However, the capacity of an individual strain to release migration inhibitory factor and IFN-gamma into the circulation did not parallel the extent either of the proliferative responses or of the release of IFN induced by lipopolysaccharide. Not all of the strains developed marked delayed footpad reactions to challenge with PPD regardless of the extent of their responses by other parameters. Delayed footpad reactions did develop in mice sensitized via the subcutaneous route, although this sensitization did not result in the capacity to release migration inhibitory factor and IFN-gamma into the circulation of individual inbred strains.

Clones of helper T cells mediate antigen-specific, H-2-restricted DTH

It is now well established that in the mouse, helper T cells and killer T cells are two distinct thymus-derived lymphocyte subpopulations, differing from each other in Lyt phenotype and H-2 restriction, among other parameters. Helper T cells are Lyt-1+ and their action in immune responses involves restriction at the H-2I region of the major histocompatibility complex (MHC). Killer cells, on the other hand, are Lyt-23+ and their activity is restricted by H-2K/D (refs 1, 3). In most instances, T cells mediating delayed-type hypersensitivity (DTH) responses share the Lyt phenotype and H-2 restriction of the helper T cell. This raises the question of whether or not helper activity and DTH can be mediated by the same activated T cell. Arguments for both views have been reported. We analysed this question using clones of specific helper T cells, which were obtained by long-term culture in vitro of in vivo primed T cells, followed by single-cell cloning. Here we show that these clones of helper T cells mediate antigen-specific and fully H-2-restricted DTH. The restricting element lies to the left of the I-B region in genetic maps of the mouse MHC.

Peritoneal exudate T lymphocytes with specificity to sheep red blood cells. IV. Fc receptors on specific peritoneal exudate lymphocytes and their role in delayed-type hypersensitivity reactions

In mice, delayed-type hypersensitivity (DTH) to sheep red blood cells (SRBC) is mediated by T cells. Peritoneal exudate T cells (PETLs) from mice optimally sensitized for DTH to SRBC form rosettes when interacted with sensitized sheep red blood cells (EA). The binding of EA to PETLs is mediated by a receptor specific for the Fc portion of the antibody (FcR). Biological activity (mediation of DTH) depends on the unreacted state of PETLs and is lost when the latter are either rosetted with EA or reacted with aggregated IgG. Transfer of EA or aggregated IgG-treated PETLs from mice with DTH to SRBC does not lead to adoptive sensitization of recipients. It is suggested that FcR found on the membrane of T cells mediating DTH play a role in the regulation of the cellular immune response to SRBC.

A functional relationship between delayed hypersensitivity and antibacterial immunity

The injection of living Listeria Monocytogenes into the site of a delayed hypersensitivity reaction in the footpads of mice resulted in inactivation of the organism. No such inactivation occurred when L. monocytogenes was injected into normal footpads. A correlation was observed between the magnitude of the delayed hypersensitivity reaction and the level of antibacterial resistance expressed within the delayed hypersensitivity site.

Local immune response to Mycobacterium lepraemurium in C3H and C57Bl/6 mice

Subcutaneous footpad inoculation of living M. lepraemurium (L.MLM) induced, in high responder C57Bl/6 mice, a local granulomatous reaction associated with the production of effector cells which stopped the multiplication of bacilli in the draining popliteal node with the concurrent development of 24--48 hr delayed type hypersensitivity (DTH). The thymus-dependent local reaction did not occur after the injection of heat-killed M. lepraemurium (HK.MLM) or after the inoculation of L.MLM in nude mice. However, HK.MLM injection interfered with the onset of the local reaction and enhanced acid-fast bacteria (AFB) counts in the draining node. In low responder C3H mice, L.MLM produced a local and delayed footpad swelling but no restriction of bacilli multiplication in the draining lymph node was observed. This unresponsiveness was not due to an overloading of the inoculum dose since doses ranging from 3 x 10(4) to 3 x 10(7) MLM did not produce any granulomatous local reaction as in C57Bl/6 mice. The injection of dead bacilli in the contralateral footpad of subcutaneously (s.c.) infected C3H mice revealed Arthus-like and 18--24 hr delayed reactions. When 10(6) L.MLM per mouse were injected intravenously (i.v.), systemic infection, measured in the spleen, was found to be less restricted in C57Bl/6 than in C3H mice. Moreover, in C57Bl/6 mice low doses of L.MLM injected i.v. delayed the local reaction at first, then enhanced footpad swelling and AFB counts in the draining nodes, indicating some acquired defect of peripheral immunity. When a high dose of L.MLM (2 x 10(8)/mouse) was injected i.v., C57Bl/6 mice died sooner than C3H mice, indicating certain discrepancies between local resistance and systemic susceptibility.

Peritoneal exudate T lymphocytes with specificity to sheep red blood cells. III. High dose of antigen induces suppressor T cells which influence the appearance in exudates of effector T cells for delayed-type hypersensitivity and helper T cells for humoral immune responses

Antisera produced in rabbits against adherent cells of rat alveolar or peritoneal lavage fluid (anti-rat alveolar macrophage sera, ARAMS, or anti-rat peritoneal macrophage sera, ARPMS) were used to detect antigenic differences between alveolar (AM) and peritoneal (PM) macrophages in an indirect membrane immunofluorescence (IMF) test. Of all sera tested, the IMF titres were higher with cells of that population which was used for immunization. These differences were found before and after exhaustive absorptions with insolubilized rat plasma, rat erythrocytes, and non-adherant rat kidney, spleen, thymus and bone marrow cells. The differences were not due to antigens specific for one of the macrophage populations, as demonstrated by cross-adsorption studies with macrophages of different localization. It is assumed that two or more macrophage specific antigenic determinants are present in different density in the two macrophage populations.

Peritoneal exudate T lymphocytes with specificity to sheep red blood cells. II. Inflammatory helper T cells and effector T cells in mice with delayed-type hypersensitivity and in suppressed mice

Peritoneal exudate cells were induced in mice 4 days after immunization with SRBC. A low dose of SRBC (10(6) i.v.) caused T lymphocytes to appear in inflammatory exudates. These cells, not only transferred DTH reactions, but also functioned as helper T cells in antibody production after transfer to syngeneic nu/nu recipient mice. After a high dose of SRBC (10(9) i.v.), very few helper T cells and no DTH transferring T cells were found in inflammatory exudates, although they were present in the spleen. It is postulated that T cells mediating DTH reactions and helper T cells behave similarly as far as those dose dependency of appearance in inflammatory exudates is concerned. A high dose of sensitizing antigen causes retention of helper and effector T cells in the spleen, in this way favouring antibody formation; low doses of antigen allow them to leave the spleen, thus favouring mediation of DTH reactions in the periphery.

Regulation of delayed-type hypersensitivity IV. Antigen-specific suppressor cells for delayed-type hypersensitivity induced by lipopolysaccharide and sheep erythrocytes in mice

Mice injected subcutaneously with 1 x 10(8) sheep red blood cells (SRBC) developed high levels of delayed-type hypersensitivity (DTH) to SRBC 4-8 days after injection. Such DTH was suppressed when 100 microgram lipopolysaccharide (LPS) was injected intravenously 1-2 days before or at the time of SRBC injection. This suppression of DTH was transferable by spleen, lymph node, thymus and bone marrow cells to sensitized or normal syngeneic recipients, but could not be transferred by serum. Suppressor cells were not induced by LPS alone or SRBC alone, and they were antigen-specific since DTH to chicken red blood cells was not affected. The suppressor cells appeared in the spleen in optimum number 3-4 days after induction. They were theta-negative and Ig-positive as judged by antiserum plus complement treatment and by Ig rosette separation. Attempts to obtain soluble suppressor factor from the suppressor cells by sonication or in vitro incubation were unsuccessful. Mitomycin C treatment of the suppressor cells completely abolished the suppressor activity. Thus, LPS, in conjunction with antigen, appears to induce a population of specific suppressor B cells which are capable of regulating T cell function.