Role of B Cells and T Cells in ACAID

Abstract

Abstract: : Purpose: Anterior Chamber–Associated Immune Deviation (ACAID) contributes to immune privilege in the eye. It is characterized by an antigen–specific, systemic suppression of delayed type hypersensitivity (DTH). ACAID is initiated in the anterior chamber (AC) where the antigen is introduced, gets captured by ocular antigen presenting cells (APC), which migrate to the spleen. In the spleen, many cells contribute to ACAID induction: CD4⁺ T cells, CD8⁺ T cells, NK T cells, γΔ T cells, and B cells. This culminates in the generation of CD8⁺ efferent suppressor T cells which inhibit the expression of DTH. This study determined if the proliferation of antigen–specific B cells is necessary for ACAID, and if γΔ T cells act upstream or downstream of B cells in ACAID. Methods: ACAID APC were generated in vitro by incubating peritoneal macrophages with TGF–ß and OVA for 24 hr. Coculture of ACAID APC with B cells induces B cells that can produce ACAID when adoptively transferred to naïve mice. Accordingly, ACAID B cells were generated in vitro and used for experiments involving the adoptive transfer of ACAID. A Local adoptive transfer (LAT) assay was used to demonstrate ACAID suppressor cells by measuring the suppression of DTH responses in the ear pinnae of mice. The capacity of ACAID APC to induce B cell proliferation was measured by incorporation of tritiated thymidine. In adoptive transfer experiments, B cell proliferation was inhibited by pretreating B cells with either mitomycin C or x–irradiation. ACAID B cells were adoptively transferred into either γΔ T cell KO mice or mice depleted of γΔ T cells with anti–γΔ antibody to determine if the obligatory role of γΔ T cells in ACAID occurred upstream or downstream of the ACAID B cell. Results: B cells proliferated in vitro when incubated with ACAID APC pulsed with OVA. B cells also proliferated in vivo following AC injection of OVA. However, inhibition of B cell proliferation prevented B cells from inducing ACAID when adoptively transferred to naïve mice. ACAID B cells adoptively transferred into γΔ T cell KO mice or γΔ T cell depleted mice were not able to induce ACAID. Conclusions: ACAID APC induce OVA–specific B cells to proliferate. ACAID B cell proliferation is necessary for ACAID induction. γΔ T cells are not needed for the generation of ACAID B cells and thus, B cells function upstream of γΔ T cells in the induction of ACAID.

Keywords: ACAID • immune tolerance/privilege • immunomodulation/immunoregulation