Regulation of the immune response by antibody. I. Suppression of antibody formation and concomitant enhancement of cell-mediated immunity by passive antibody

T cell biasing by activated dendritic cells

We have previously reported that the ligation of FcgammaRs on activated macrophages affected their production of cytokines and their ability to influence T cell activation. Dendritic cells (DC) are important APCs that also express FcgammaR. In the present work, we sought to determine whether DC responded to immune complexes in a manner similar to macrophages. We confirmed that activated murine DC produced IL-12, and, as a result, induced naive T cells to produce primarily IFN-gamma upon stimulation. However, DC activated in the presence of immune complexes shut off their production of IL-12p70 and induced a Th2-like cytokine response. Thus, DC respond to immune complexes by altering their cytokine production, which, in turn, influences T cell responses. A DC transfer experiment was performed to determine the extent that APC exposure to immune complexes could influence adaptive immune responses. Vaccination of mice with Ag, along with DC that were activated in the presence of immune complexes, resulted in higher levels of Ag-specific IgG1 Ab, relative to mice that were vaccinated with activated DC and Ag alone. The mechanism by which DC altered their cytokine production in response to immune complexes was different from macrophages. Macrophages down-regulated the transcription of both the p40 and p35 subunits of IL-12, whereas DC decreased only p35 expression. We conclude that APCs expressing FcgammaR on their surface can respond to immune complexes by shutting off IL-12 biosynthesis, to prevent the Th1-type T cell biasing that normally accompanies innate immune activation.

Cutting edge: biasing immune responses by directing antigen to macrophage Fc gamma receptors

An immune response can deviate toward either a Th1- or Th2-like response. In this work we examine the contribution that activated macrophages and IgG Abs make toward this deviation. The use of activated macrophages as APCs resulted in a strong polarized T cell response that was predominated by IFN-gamma. However, when Ag was targeted to FcgammaRs on these macrophages, the T cell response was reversed and biased toward a Th2-like response. This Th2-like phenotype was stable and was retained when the T cells were subsequently restimulated under nonbiasing conditions. The T cell biasing and its reversal via FcgammaR was also observed in vivo. Mice vaccinated with IgG-opsonized OVA made high levels of IgG Ab of the IgG1 isotype. These studies demonstrate that the ligation of FcgammaR on activated macrophages can reverse the Th1 biasing that occurs as a result of innate immune responses to microbial products.

Immune complex-mediated enhancement of antibody responses without induction of delayed-type hypersensitivity

Immunoglobulin (Ig)G and IgE antibodies enhance the humoral response in vivo to soluble antigens with which they form complexes. In vitro, antigen is targeted to B cells by IgE antibodies and to macrophages and dendritic cells (DCs) by IgG, thus leading to increased antigen presentation to specific T cells. Possibly these mechanisms are also responsible for antibody-mediated enhancement in vivo. We now address the question of whether IgG- and/or IgE-antigen complexes can prime for delayed-type hypersensitivity (DTH), a reaction known to require primed T helper (Th)1 cells. Mice were immunized with IgG-anti-2,4,6-trinitrophenyl (TNP)/BSA-TNP or IgE-anti-TNP/BSA-TNP. Mice given BSA-TNP alone or BSA-TNP in complete Freund's adjuvans (CFA) were used as controls. DTH and IgG-anti-BSA levels were measured after subsequent challenge with BSA. A potent BSA-specific antibody response was induced by IgE- or IgG-complexed antigen as well as by CFA/antigen but DTH-reactions were only observed in mice immunized with CFA/antigen. Both IgE and IgG enhanced the production of BSA-specific IgG1, IgG2a and IgG2b, although the most pronounced enhancement was seen in the production of IgG1. These findings suggest that Th2 cells rather than Th1 cells are involved in the immune response to IgG- and IgE-immune complexes.

Vaccine strategies: selective elicitation of cellular or humoral immunity?

The discovery of immunoregulatory cytokines and the fact that they modulate the cellular and humoral arms of the immune system, generally in opposing directions raises fundamental questions concerning vaccine development. Because antibiotic-resistance infectious organisms are appearing at an increasingly rapid rate, more emphasis will need to be placed on prevention of infection/disease via immunization and less on post-infection antibiotics. To accomplish this task effectively, immune regulation should be integrated into vaccine design. Here we consider the opposing potentials of cytokine-regulated cellular and humoral immunity, and question whether the "best of both worlds' is possible or desirable.

Immune deviation: a historical perspective

In this paper I have reviewed my early studies, between 1966 and 1976, on the phenomenon of immune deviation. Initially summarized are experiments with different forms of the flagellin antigen from Salmonella adelaide which established the inverse relationship between delayed-type hypersensitivity (DTH) and antibody formation. Based on the flagellin studies, many of the key factors which determine whether an antigen will induce either DTH or antibody formation were delineated. These factors are just as relevant today as they were 25 years ago. Subsequent analyses at the cellular level demonstrated that different T cell subsets mediate DTH and T cell help and maintain immune deviation by suppressor mechanisms. A number of fundamental questions raised by this early work remain unanswered and are discussed. These include the nature of the primary signalling events which initiate immune deviation, the role of B cells in the deviating process and the mechanism by which CD8+T cells suppress antibody production.

Immunological signals which control T cell responses

A number of identifiable immunological parameters can influence the elicitation and regulation of antigen-specific inflammatory responses to immunogenic epitopes. Injection of antigen in vivo can lead to the activation of type IV hypersensitivity responses, or to the induction of immunological tolerance to that antigen. We have used the hapten trinitrophenol as a model system for studying the factors which influence the generation and regulation of hypersensitivity responses to immunogenic epitopes in vivo. The generation of hypersensitivity or tolerance to trinitrophenyl depends on a number of immunological factors, including the form of the antigen, the route of immunization, and the presence of immune complexes of antibody and antigen on the surface of the antigen-presenting cell. Immunization with trinitrophenyl resulting in unresponsiveness can be the result of either the inability to prime inflammatory cells in vivo or the induction of suppressor T cells.

Antigen-specific augmentation of delayed-type hypersensitivity by immune serum factor in mice

The serum from C3H/He mice immunized with chicken erythrocytes (CRBC) in complete Freund's adjuvant contained a factor able to augment delayed-type hypersensitivity (DTH) antigen specifically, when transferred into naive syngeneic recipient mice before their sensitization with CRBC. This activity in immune serum appeared on Day 4 and reached a peak on Day 8 after immunization, and was enhanced when donor mice were treated with cyclophosphamide (CY) 2 days before immunization. The ability of recipient mice to respond to this factor was enhanced by CY treatment of these mice 4 days before being transferred. This factor could be discriminated from conventional antibodies. Production of this factor in the serum donor and the expression of its activity in transferred recipient was mediated by a T-cell subset which showed a low degree of thymus dependency in ontogenic development.

Potentiation of the rat delayed-type hypersensitivity reaction by the Fc portion of human IgG1

Fc fragments derived from a human IgG1 myeloma protein potentiate the rat delayed-type hypersensitivity (DTH) reaction to antigen challenge. Lewis rats immunized with heat-killed tubercle bacilli give augmented DTH reactions to the purified protein derivative of tuberculin when Fc fragments are included in the challenge dose. Similar potentiation of DTH by pFc' fragments indicates that the active site is located in the CH3 domain of IgG1. Histologic evaluation of the augmented reaction sites revealed predominantly mononuclear cell infiltrates characteristic of DTH reactions. Skin tests of tubercle bacilli-sensitized rats with an unrelated antigen and/or Fc fragments fail to elicit significant reactions. Augmentation of the DTH reaction to purified protein derivative is restricted to the Fc or pFc' region fragments since intact monomeric IgG1, Fab fragments, and bovine serum albumin were all shown not to be active potentiators. The DTH reaction of ovalbumin-sensitized rats was similarly augmented when Fc fragments were included with a challenge dose of ovalbumin, thus supporting the general nature of the phenomenon. These results support the concept of Ig molecules as multifunctional proteins that can not only serve effector functions but also participate in the regulation of immune responses.

Rubella and juvenile chronic arthritis

A 9-year-old boy with a clinical illness similar to juvenile rheumatoid arthritis was found to have rubella virus in the synovial fluid. There was complete remission of symptoms after 3 months. The role of rubella virus as a possible possible aetiological agent in juvenile rheumatoid arthritis is discussed.

Regulation of delayed-type hypersensitivity. V. Suppressor cell memory in antigen-specific suppression of delayed-type hypersensitivity to sheep erythrocytes

Mice printed i.v. wit 10(9) sheep red blood cells (SRBC) produce antigen-specific T suppressor (Ts) cells which inhibit both the induction and the expression of delayed-type hypersensitivity (DTH). These Ts cells are detectable in the spleen and lymph nodes 3-5 days after priming but are largely absent by 6 days. The transient detectability of the Ts cells contrasts sharply with the profound antigen-specific suppression which persists in primed donor mice for at least a year. Evidence is presented that this long-term impairment of DTH is maintained, at least in part, by memory Ts cells which are Thy-1+, cyclophosphamide-resistant and antigen-specific. Although they appear to be co-induced with the short-lived primary Ts cells and localize initially in the lymphoid organs, they are present in the long-lived circulating pool of T cells and can be adoptively transferred by celomic parabiosis. Memory Ts cells are readily reactivated by lower doses of SRBC which would induce T effector cells rather than Ts cells in naive animals. Reactivated memory Ts cells seem to generate a population of antigen-specific secondary Ts cells which again localizes in the lymphoid organs and can adoptively suppress the induction and expression of DTH to SRBC.

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.

Local and systemic immunity to influenza infections in ferrets

To establish whether immunity to influenza infection in the ferret is local or systemic, two sites of challenge were utilized: the nose and the anatomically isolated tracheal pouch. Infection of either site did not spread to the other site, and challenge of either site resulted in seroconversion by 13 days. Simultaneous challenge of both sites 21 days after the primary infection revealed that prior infection of the pouch prevented subsequent reinfection of the pouch, but not infection of the nose. Thus, systemic immunity did not prevent the initiation of nasal influenza infection in the ferret. However, the duration of virus shedding from the nose was reduced to half of that seen when ferrets were infected for the first time, showing that the prior pouch infection did lead to a more rapid recovery from the subsequent nasal infection. Passively administered anti-influenza antibody did not prevent or modify the nasal infection, but it did prevent the pouch infection. This is consistent with the observation that an initial infection of the nose prevented pouch infection upon challenge 21 days later. The prior nasal infection also prevented the subsequent nasal infection. These data suggest that immunity to acquisition of influenza infection in the ferret is a local phenomenon, whereas recovery from active infection is influenced by systemic immune mechanisms.

Lack of a correlation between cell-mediated immunity to the carrier and the carrier-hapten helper effect

The relationship between cell-mediated immunity to the carrier and the carrier-hapten helper effect was studied in the rat by using three forms of the carrier which differed in their capacity to induce carrier-specific delayed-type hypersensitivity. The three carriers were polymerized flagellin (POL), flagellin (FIN), and acetoacetylated flagellin (AFIN), which induced FIN-specific delayed-type hypersensitivity in the order AFIN > FIN > POL. Helper cells for the anti-DNP antibody responses to a range of DNP-FIN conjugates appeared to be almost inversely related to cell-mediated immunity to the carrier, being in the order POL > FIN =/> AFIN. These differences occurred whether the carriers were injected in saline or FCA, but were less pronounced with the heavily DNP-conjugated flagellins.