Differences in epitopes recognized by T cells during oral tolerance and priming

Importance of dose of type II collagen in suppression of collagen-induced arthritis by nasal tolerance

OBJECTIVE

To determine the influence of the dose of collagen given nasally on the induction of specific mucosal tolerance in collagen-induced arthritis.

METHODS

The severity of clinical arthritis induced in DBA/1 mice was studied after the nasal administration (before disease induction) of 1 of 4 doses (across a 2-log range) of bovine type II collagen (CII). Parameters of immunity included lymphocyte proliferation and cytokine production in vitro in response to antigen stimulation, and the production of anticollagen IgG antibody subclasses.

RESULTS

The 3 highest doses (20, 80, and 320 microg) ameliorated disease severity, whereas the lowest dose (5 microg) aggravated disease. These findings correlated well with antigen-specific T cell proliferation and cytokine and antibody production. T cell proliferation was suppressed by the higher doses of CII, whereas the low dose enhanced T cell proliferation, indicating it primed the T cells. Suppression of T cell proliferation could be overcome by the addition of exogenous interleukin-2 (IL-2) to these cultures. Decreased T cell proliferation was associated with suppression of both Th1 (interferon-gamma [IFNgamma]) and Th2 (IL-4) cytokines and all the subclasses of anticollagen IgG in mice receiving 20, 80, or 320 microg of collagen. Overall, the highest dose of collagen (320 microg) was less effective at suppressing the immune response and disease than the 20-microg or 80-microg doses. There was an increased production of antibodies of all IgG isotypes, and of the Th1-associated cytokines IFNgamma and IL-2, in animals that had received the lowest dose of 5 microg collagen nasally.

CONCLUSION

Nasal administration of antigens is effective in inducing tolerance and reducing disease severity, but the effects are dose dependent. Low doses can prime the immune system and aggravate disease; high doses may not suppress disease. Suppression of the immune response, which correlates with suppression of disease, is not obviously associated with a type I to type II T cell switch, but rather with an overall suppression of both forms of T cell response, with a potential role for anergy of T cells in this process.

Abrogation of oral tolerance by feeding encapsulated antigen

Results from previous studies have indicated that suppression of immune responses cannot be abrogated once oral tolerance has been established. Using a new methodology, OVA was encapsulated and fed to tolerized BDF1 mice. Results from these studies indicated that although IgG2a titers remained low, total IgG and IgG1 antibody titers were no longer suppressed compared to controls. Furthermore, in vitro splenocyte proliferation was not significantly suppressed in tolerized mice fed encapsulated OVA. To determine whether oral tolerance could be abrogated in other strains of mice, BALB/c mice were tolerized and fed encapsulated OVA. Results from these studies indicated that IgG2a as well as IgG1 and total anti-OVA antibody titers were no longer suppressed. Although splenocyte proliferation did remain significantly suppressed in these mice, IFN-gamma and IL-4 levels were no longer decreased. To the best of our knowledge, this is the first time that abrogation of an established oral tolerance has been demonstrated.

Immune responses to dietary antigens: oral tolerance

The concept of immunologically mediated tolerance to food antigens through exposure to mucosal antigen has been the subject of continuous scientific debate. After a decline in interest in the mid-1980s, oral tolerance has again attracted the attention of immunologists. Here, Stephan Strobel and Allan Mowat discuss how this central immunological principle has potential new therapeutic applications for the treatment of autoimmune, inflammatory and possibly food-allergic diseases.

Erythrocytes enhance the immunogenicity of oral vaccination with gamma irradiated influenza virus: increasing the dose of irradiation results in a significant diminution of lung IgA response

Previous studies have demonstrated that the ability of gamma-irradiated whole influenza virus to prime for specific anti-influenza antibody responses was dramatically enhanced when delivered in a complex with chicken red blood cell ghosts (cRBC). The purpose of this study was to investigate the effect of increasing the dose of gamma irradiation used to inactivate A/Queensland/6/72 virus on the ability of the virus-cRBC complex to prime for specific influenza responses. Spleen cell proliferation studies confirmed the enhancing effect of the cRBC carrier for oral vaccination with irradiated virus. Cells from mice vaccinated with 30 kGy-irradiated virus only did not respond to influenza stimulation in vitro, whereas cells from mice vaccinated with irradiated virus+cRBC showed significant increases in proliferation to antigen exposure. No significant antibody response or challenge virus clearance was observed in mice orally vaccinated with irradiated (13.1 or 30 kGy) virus alone, even when the dose was increased significantly. Oral vaccination with live virus (+/-cRBC) primed for significant influenza specific IgA responses in the lungs, in addition to IgG responses in the lungs and sera. The dose of irradiation used to inactivate the virus was found to be critical to the profile of antibody response when the virus was delivered in a complex with cRBC. Oral vaccination of Swiss mice with 13.1 or 30 kGy virus (+cRBC) primed for significant serum and lung IgG responses. Lung IgA responses for 13.1 kGy+cRBC vaccinated mice were detected, but 30 kGy+cRBC vaccinated Swiss and CBA/H mice had no significant lung IgA response. The abrogation of IgA response, however, did not lessen the clearance of live challenge virus in outbred mice, suggesting a primary role for IgG and/or CTL response in the control of influenza virus infection post oral vaccination. To ensure direct comparison of virus alone and virus+cRBC treatments, the concentration of virus complexed to the cRBC was determined.