IMMUNOLOGIC TOLERANCE AFTER SPECIFIC IMMUNIZATION

Induction in human allograft recipients of unresponsiveness to anti-lymphocyte globulin

The observations presented here confirm previous reports that polyclonal ALG prepared at the University of Minnesota or ATGAM of The Upjohn Co., administered as described, rarely induced sensitization of patients to the horse gamma globulin. In addition, the phenomena of transient antibody production prior to the onset of unresponsiveness and the induction of unresponsiveness in individuals with preexisting antibodies were observed.

Adoptive transfer of suppression of arthritis in the mouse model of collagen-induced arthritis. Evidence for a type II collagen-specific suppressor T cell

This study details the suppressive mechanism involved in the antigen-specific suppression of collagen-induced arthritis. Intravenous injection of 500 micrograms of soluble native type II collagen 3 d before immunization with native type II collagen emulsified in complete Freund's adjuvant resulted in animals with decreased in vitro cellular and humoral immune response to native and denatured type II collagen compared with control groups. Control groups were composed of animals preinoculated with saline and type I collagen and established the antigen-specific nature of the observed suppression. Mice with reduced immune responses to type II collagen also were observed to portray little or no erythema and edema associated with collagen-induced arthritis. Adoptive transfer experiments established the requirement of T cells for the suppression of collagen-induced arthritis. Analysis of the phenotype of responding splenic cells in chronic immunotherapeutically suppressed mice in vitro revealed that responding cells were Ly1-2+ (suppressor/cytotoxic) T cells. On the other hand, the cellular phenotype of T cells responding to type II collagen in nonsuppressed collagen-induced arthritic mice was Ly1+2- (helper/inducer T cells). The data indicate that type II collagen-specific T cells are generated on intravenous inoculation of soluble native type II collagen. These cells are observed in type II collagen-immune animals, which are nonarthritic and portray reduced humoral and in vitro cellular immune response to type II collagen. This study suggests that specific suppression of immune responses to type II collagen by T-suppressor cells can be immunotherapeutic in certain forms of arthritis.

Selective and specific inhibition of 24 hour skin reactions in the guinea-pig. 3. Depression of cytophilic and haemolytic antibodies by pretreatment with antigen and the effect of irradiation

Dvorak and Flax (1966) and others reported that adult guinea-pigs pretreated with soluble antigens showed depressed immune responses following immunization with the same antigens in Freund's complete adjuvant. These depressed immune responses included haemolytic and cytophilic antibody and delayed hypersensitivity as well as antibody measured by passive cutaneous anaphylaxis and haemagglutination. This communication describes further studies on the effect of pretreatment with alum precipitated bovine γ-globulin rather than soluble antigen. Guinea-pigs given 1 mg of alum precipitated bovine γ-globulin prior to immunization with 50 μg bovine γ-globulin (BGG) in Freund's complete adjuvant show depressed haemolytic and cytophilic antibody and delayed hypersensitivity. This depression is immunologically specific as pretreatment with alum precipitated egg albumin does not depress immune responses to bovine γ-globulin. In contrast, antibody measured by passive cutaneous anaphylaxis and haemagglutination is either unaffected or raised.

Similarly, pretreatment with sheep red cells reduces the cytophilic antibody response to sheep red cells in Freund's complete adjuvant.

This depression is long lasting and 1 mg alum precipitated BGG depressed the haemolytic antibody response to BGG in adjuvant given 6 months later and the delayed hypersensitivity response to BGG in adjuvant given 9 months later. Alum precipitated BGG given up to 6 days after immunization with BGG in adjuvant caused some depression of haemolytic antibody. However, this depression was transient and much less than the long lasting depression caused by pretreatment with alum precipitated BGG 7 days before immunization with BGG in adjuvant.

The effect of irradiation followed by alum precipitated BGG on the immune responses to BGG in Freund's complete adjuvant was also studied. 300 r depressed haemolytic and haemagglutinating antibody but had no effect on cytophilic antibody or delayed hypersensitivity. There was no synergy between irradiation and pretreatment with BGG; the depression of immune responses caused by irradiation followed by alum precipitated BGG was no greater than the depression caused by the more effective agent when given alone.

Kinetics of the proliferative response to antigen in vitro of rabbit lymph node cells taken at various times after immunization

The antigen stimulation of thymidine uptake by immune rabbit lymph node cells in vitro was studied. The kinetics of the response varied depending on the time between immunization and culture. Cultures set up early after immunization showed a peak response over day 1–2 of culture while those set up late after immunization showed a peak response over day 3–4.

Studies using the metabolic inhibitor BUDR suggested that this is due at least in part to a larger recruitment of cells into the response during the third day of culture when lymph node cells taken late after immunization were used.

Removal of antigen from cultures after brief exposure of cells at 4° reduced the magnitude but did not eliminate the proliferative response, suggesting that some antigen is specifically bound to the cells in the cold. Readdition of antigen restored normal reactivity.

Holding cells at 4° for 4 hours without antigen had no effect on their response to subsequent addition of antigen. However, if cells were held at 4° for 3 hours with antigen present a severe degree of depression of subsequent thymidine incorporation was observed in some but not all experiments. This depression of responsiveness was interpreted as an in vitro phenomenon comparable to immunologic tolerance.

The X-Y-Z scheme of immunocyte maturation. V. Paralysis of memory cells

A concentration of 5 mg/ml bovine serum albumin (BSA) prevents the in vitro elicitation of a secondary response in primed rabbit popliteal lymph nodes, if it is left in contact with the node fragments for the first 6 days of culture. No antibody formation can be detected at any time during the culture period in most cases, although occasional fragments are resistant to inhibition. Reducing the exposure time to the first 3 days of culture delays the peak of the antibody response. The inhibition is antigen specific. Reconstruction experiments demonstrate that the inhibition is not due to antigen masking of the antibody. Even shortly after optimal stimulation, the addition of 5 mg/ml BSA to the fragments was not able to prevent a normal antibody response. The implications of these findings are that (a) a high antigen concentration suspends the memory cell in a reversibly paralyzed state, (b) memory cells have a heterogeneous susceptibility to inhibition, (c) once induced, the antibody response cannot be inhibited by antigen overloading, (d) unresponsiveness in a primed animal can be due to either exhaustion of the memory cell population or paralysis of the memory cell.

Immunological responsiveness following the continuous circulation of soluble antigen--antibody complexes

Following the continuous circulation of soluble bovine serum albumin—anti-bovine serum albumin complexes, adult rabbits rapidly lose the ability to synthesize specific antibodies to bovine serum albumin (BSA). This tolerant state appears to be similar to that produced in adult rabbits by large doses of antigen.

(1) The animals showed delayed elimination of injected [¹²⁵I]BSA.

(2) Immunization with human serum albumin (HSA) enhanced the elimination of intravenously injected [¹²⁵I]BSA.

(3) BSA failed to stimulate the in vitro incorporation of [¹⁴C]thymidine by spleen cell suspensions from these tolerant animals.

(4) Although some animals made a small amount of anti-BSA antibodies in vivo there was no response in vitro to the same antigen.

The X-Y-Z scheme of immunocyte maturation. IV. The exhaustion of memory cells

A set of conditions has been described under which primed rabbit lymph nodes produce a secondary antibody response upon in vivo stimulation with a large dose of antigen, but are subsequently "exhausted;" that is, lymph node cultures prepared at intervals following the booster injection cannot be re-stimulated to display tertiary responses. Rabbits given 100-fold less antigen in the booster inoculum were able to give a tertiary response upon in vitro challenge. The system used permits neither induction nor continuation of a primary response to BSA in vitro. Since it could be demonstrated that no memory cells were generated by the booster injection within the intervals between in vivo injection and culture, the tertiary response in nonexhausted nodes must have been due to residual memory cells which remained untriggered by the in vivo booster injection. The unresponsive state was not caused by antibody feedback. These results are interpreted to mean that a population of memory cells can be exhausted by a supraoptimal dose of antigen, rendering the node temporarily incapable of further response. This implies that long-lived memory is not due to asymmetric division of memory cells. The source and fate of memory cells is discussed with regard to this evidence.

Studies on the induction of immunological unresponsiveness to pneumococcal polysaccharide in mice

1. Comparison of dose-response curves indicated that preimmunized animals were slightly more susceptible to the induction of immunological paralysis with pneumococcal polysaccharide than were normal mice. The results also indicated that the paralysis threshold was unaltered by preimmunization. 2. Transient desensitization of immunized mice could be achieved by an amount of polysaccharide far less than that required to induce paralysis. 3. A transient phase of weak immunity was detected prior to the onset of paralysis when induced by relatively low paralyzing doses of polysaccharide. 4. No "low dose" zone of paralysis (analogous to that obtainable with certain protein antigens) could be elicited with pneumococcal polysaccharide. 5. Massive proliferation of lymphoreticular tissues induced by Corynebacterium parvum failed to raise the threshold for paralysis induction, but amplified the immune response over the entire dose-response curve. Similarly, C. parvum failed to abrogate an established state of paralysis. The results suggest that the induction of polysaccharide paralysis is related to the concentration of antigen in the animal and is not modified by the number of immunologically competent cells.

Role of the thymus in tolerance. 3. Tolerance to bovine gamma globulin after direct injection of antigen into the shielded thymus of irradiated rats

Rats subjected to high doses of whole-body irradiation, with simultaneous shielding of the thymus or spleen, recovered at 3 wk the ability to develop delayed sensitization and to form hemagglutinating and precipitating antibody following foot-pad injection of BgammaG in complete adjuvant. Injection of BgammaG into the shielded thymus immediately after irradiation, in amounts between 20 gammag and 40 mg, inhibited these response to later challenge partially or completely. A comparable effect on immune responses to BgammaG was not seen after injection of heterologous antigen (Ea) intrathymically, BgammaG intraperitoneally, or BgammaG into the shielded spleen. However high doses (20 or 40 mg) of antigen given by the latter routes resulted in some diminution of later response. Arthus reactivity recovered partially in the spleen-shielded group and was readily suppressed by intrasplenic administration of antigen.

Split tolerance affecting delayed hypersensitivity and induced in mice by pre-immunization with protein antigens in solution

Adult immunocompetent mice vaccinated with protein antigens in water-in-oil emulsion so as to develop immediate and delayed hypersensitivities resist developing the latter if they are treated with the immunizing antigen in aqueous solution before or during the sensitization period. If the treatments are given during or after vaccination this resistance is directly proportional to their intensity and inversely proportional to the degree of hypersensitivity which has developed when they are begun. But when the treatments are given before vaccination such split tolerance is more pronounced and seems to be directly proportional more to the degree of humoral antibody production existing at the time of vaccination than to the intensity of treatments. The characteristics of this antigenically specific selective unresponsiveness suggest that it may result from a competitive maturation or differentiation of primitive immunocytes: upon exposure to protein antigens in forms not readily able to induce delayed hypersensitivity, the potential functions of these immunocytes for making circulating antibodies may be pre-empted at the expense of such capacity to develop into cells making the antibody of delayed hypersensitivity.

Specific Inhibition of Antibody Formation by Passively Administered 19S and 7S Antibody

Intravenously administered 7S antibody is more effective than 19S antibody in inhibiting the formation of antibody to bacteriophage X174. Since considerable amounts of 7S antibody are needed for inhibition, serum antibody formation may act as a "feedback" mechanism to prevent hyperimmunization.