Correlations between rat strain, agglutinating antibody responses in serum or saliva and caries incidence, previously observed in Harvard rats mono-associated with Streptococcus faecalis and given diet L128 and 5 per cent sucrose added to drinking water, were not found when experiments were repeated with the low-sucrose diet 305. Mono-association with either Streptococcus mutans 6715 or Strep. faecalis ND547 produced extensive caries in caries-susceptible (HCS) rats and little or no caries in resistant (HCR) ones, but caries incidence did not relate to levels of agglutinating antibodies in serum or saliva. There was markedly less serum antibody to Strep. faecalis in the HCR rats and more antibody in HCS rats, when compared to previous results, but this did not affect caries scores in either strain. No agglutinating antibody to Strep. mutans was detected in serum and indefinite antibody appeared in saliva. Under these conditions, the ability to produce an agglutinating antibody response did not appear to play a role in caries resistance.

Rabbit dams fed 0.1% BSA for various periods before and during lactation produced anti-BSA of low avidity and IgG isotype in serum and milk. Milk anti-BSA and IgG concentrations were one-third to one-half of those in the serum. At birth, kits had IgG and anti-BSA serum concentrations approximately equal to their dams. Both fell rapidly for the first 10-20 days, levelling off at about 1 mg IgG/ml. Kits born to unimmunized dams and suckled by dams with anti-BSA in the milk showed increasing anti-BSA in serum for the first 12-16 days, falling by 20 days. Foster-suckling on immunized dams beginning at various times after birth showed antibody uptake from birth through 12 days of age. Thus immunoglobulins are among factors absorbed from milk that have potential for regulating the immune responses of rabbit neonates.

The effect of feeding xenoserum (xs) on cytolytic cell activity induced by parenteral injection was examined in C3H/N mice. Spleen cells were cultured with xs and then assayed for cytolytic activity against a panel of 51Cr-labeled YAC-1, AKR-A, or P815 target cells. Prior feeding resulted in significant suppression of responses stimulated by injection and culture. The induction of these responses was antigen specific for xs whereas the effector stage represented polyclonal activation of cytolytic cells. Some effector cells were lysed by either anti-Lyt 2 or anti-NK- 1.2 and complement and some were blocked by anti-Lyt 2 or anti-T200 in the cytotoxicity assay. Thus, both cytolytic T and NK-like cells were suppressed by antigen feeding. Activity of TH cell-derived factors which enhance cytolytic activity (“promoter” factor, interferon, and interleukin 2) also was diminished in culture supematants of cells from mice fed soluble antigens. The conclusion that polyclonal cytolytic responses induced by soluble antigen can be regulated by prior enteric stimulation is made.

The effects of local antigenic exposure on the responsiveness of systemic T cells were evaluated after C3H mice were given drinking water containing 6% bovine serum albumin (BSA) for 10 days and challenged sc with 1.0 mg BSA in adjuvant 28 days after the initiation of antigen feeding. During the first 28 days, no evidence of in vitro antigen-induced proliferation [( 3H]thymidine incorporation) was detected in whole lymphocyte populations from the peripheral lymph nodes (PLN), spleen, or mesenteric nodes. In contrast, PLN cells treated with anti-Lyt-1 plus complement (C) had a significant proliferative response only if the cells were obtained during the first 6 days of antigen ingestion. Lymphoid cells from the same animals, treated with anti-Lyt-2 and C, did not respond to antigen. Two or 4 days after the injection, given on day 28, whole PLN cell populations from antigen-fed mice showed proliferation. No response was observed with PLN cells obtained 8 days after injection. Shortening the interval between the initiation of feeding and parenteral challenge partially restored proliferative responses detected 8 days after injection. Cultures prepared 4 days after simultaneous oral and parenteral antigenic exposure showed proliferation equal to or greater than cultures from mice that received only the injection. These data show that systemic T cell responsiveness is not eliminated by ingestion of soluble antigen, but rather is modulated in a manner previously detected in the humoral immune system.

Peripheral lymph node cells from C3H mice that were fed and injected with bovine serum albumin (REG cells) demonstrate an impaired proliferative response to antigenic stimulation in vitro compared to cells from mice only injected with BSA. To determine whether suppressor cells contributed to this enterically induced impairment of systemic T cell responses, REG cells were pretreated with various monoclonal antibodies and complement (C), and were then co-cultured with antigen-reactive indicator T cells (IND) from parenterally immunized mice. Proliferation of IND cells [( 3H]thymidine uptake) was suppressed only if REG cells were treated with anti-Lyt-2 and C before co-culture. The ability of anti-Lyt-1 plus anti-Lyt-2 and C treatment to abrogate suppression suggested that the suppressor effect was due to an Lyt-1+, 2- REG cell. Suppression was independent of Lyt-2+ IND cells, and was observed at different antigen concentrations, cultivation times, and cell densities. The cells responsible for suppressor activity were radiosensitive, nylon wool nonadherent, and antigen specific. These data suggest that an Lyt-1+, 2- T cell could be an important component in mediating enterically induced regulation of systemic T cell responses.

Following ingestion of bovine serum albumin (BSA), human infants and rabbits synthesize circulating anti-BSA. Using a similar protocol, the serum antibody response was examined in C3H mice offered 0.1, 1.0 or 6.0% BSA for 10 or 56 days. Sera from these animals contained similar amounts of antigen, but anti-BSA was undetectable. Half the animals in each group were subsequently injected i.v. with 50.0 mg BSA. Mice fed 1.0 or 6.0% BSA were unresponsive to this challenge, but animals fed 0.1% BSA responded comparably to i.v. immunized, non-fed controls. The remaining animals in each group were injected s.c. with 1.0 mg BSA in adjuvant. Most of these mice produced circulating anti-BSA. However, these responses were significantly reduced relative to s.c. immunized, non-fed controls. Hyporesponsiveness again was least after 0.1% BSA ingestion. CF1 mice and BN, HCR and HCS rats fed 0.1% BSA for 56 days also did not produce circulating antibodies during ingestion, and almost all were hyporesponsive after parenteral challenge. Suppression of specific antibody responses also was observed in C3H mice fed and challenged with diphtheria toxoid. The data suggest that under identical experimental conditions, ingestion of soluble protein antigens induces a state of systemic hyporesponsiveness in mice and rats in contrast to the systemic immunity demonstrated in human neonates and adult rabbits.

The contribution of bronchus-associated or gut-associated lymphoid tissues to the development of specific immunologic reactivity in lactating mammary glands was studied by evaluating the effect of the nature of the antigen and the route of immunization on milk antibody content. Groups of pregnant rabbits were immunized with respiratory syncytial virus (RSV) and bovine serum albumin (BSA) administered i.v., per oral (p.o.) or transtracheal (i.t.) routes. The response to RSV was characterized by the regular appearance of IgA anti-RSV in the colostrum, milk, bronchial, and intestinal secretions following p.o. or i.t. immunization, but not after i.v. immunization. RSV-specific IgG appeared in the colostrum, milk, and serum regardless of the route of immunization. On the other hand, the response to BSA by all three routes of immunization was characterized by the appearance of anti-BSA in serum, colostrum and milk which was solely associated with IgG. The anti-BSA isotype did not change during the 30-day nursing period and was not affected by BSA ingestion before or during pregnancy or during nursing. If BSA was reintroduced after 20 days of nursing, a sharp rise in the Ab content of milk occurred in p.o. but not i.v. immunized dams. This increased anti-BSA was also of the IgG isotype. These observations suggest that the isotypes of specific Ab responses in the lactating mammary gland of the rabbit may be determined by the physical and chemical nature of the antigens contacted on respiratory or intestinal mucosal surfaces.

Immune responses following antigen ingestion vary from stimulation to suppression depending on animal species, antigen, and experimental protocol. Young adult rabbits were given either 0.02% diphtheria toxoid or 0.1% bovine serum albumin in drinking water for 10-day periods, a protocol previously found to immunize human infants fed bovine serum albumin. Specific serum antibody was detected by radioimmunoassay in 10 of 13 rabbits fed diphtheria toxoid for 10 days and 11 of 13 rabbits fed bovine serum albumin. Response to oral diphtheria toxoid in some animals was equal to that after an injection of alum-precipitated diphtheria and tetanus toxoids. All rabbits fed a second course of either antigen showed an enhanced, rapid rise in antibody concentration. Avidity of the antibody also increased markedly, suggesting that priming and memory had been established during the first feeding. Similar anamnestic responses occurred in animals given a parenteral challenge after ingesting antigen. One month after administration of diphtheria toxoid, no significant difference in serum antibody levels was present between unfed animals challenged with diphtheria-tetanus toxoids and although avidity of the antitoxin was higher in fed animals. Antibody activity could be detected only in the immunoglobulin G serum fractions with either antigen. These responses suggest that oral immunization protocols using protein antigens can be adapted for use against toxins causing disease.

Immunity against diphtheria (D) is poorly understood since protection is a complex interaction between host and environment and there are technical problems with existing antitoxin assays. Using a radioimmunoassay, antitoxin was detected in sera from premature infants after 33 weeks of gestation and the maternalcord serum ratio of 18 term infants was 0.8 ±0.3 (1 SD), Following the first DTP (7.5 Lf units D toxoid) significant antitoxin production was not detected. This relatively poor antigenicity was found in the absence as well as presence of maternal antibody. A rise in antibody concentration and affinity was found after the 2nd, 3rd, and 4th injections. More than four injections did not alter concentration and affinity of the antitoxin or the rate of decline in concentration. Correlation with recent epidemiologic studies suggests that a serum contained a protective concentration of antitoxin if it bound more than 150 ng D toxin N/ml of serum. By this criteria only 74% of children who received 3 immunizations and 84% of children who received 4 or more were protected. Among the 188 children studied 34% had appropriate immunizations for age. These observations suggest that the immunologic status of urban children to D is inadequate and an improvement in patient education and immunization practices is needed, (supported by AI-07854)