CD25⁺, interleukin‐10‐producing CD4⁺ T cells are required for suppressor cell production and immune privilege in the anterior chamber of the eye

Abstract

SUMMARYAn important factor in the establishment of ocular immune privilege is the dynamic down regulation of T helper 1 (Th1) immune responses that occurs in response to antigens delivered intraocularly; a phenomenon that has been termed anterior chamber-associated immune deviation (ACAID). ACAID is characterized by the generation of splenic regulatory cells that inhibit the expression of delayed-type hypersensitivity. Previous studies have shown that antigens introduced into the anterior chamber of the eye induce the generation of a CD4Tcell population that suppress the induction of Th1 immune responses and the appearance of a second population of CD8T regulatory cells that suppresses the expression of Th1 in¯ammatory responses ( efferent suppressor cells). Experiments described here characterized the function of the CD4ACAID suppressor cell population and its effect on the generation of CD8 efferent suppressor cells that inhibit the expression of DTH in situ. Both in vivo and in vitro experiments demonstrated that CD4 T cells are required for the generation of CD8 efferent suppressor cells. CD4 T cells do not require cell contact with CD8 T cells; instead they produce soluble IL-10 that is suf®cient for the generation of ACAID suppressor cells. Finally, the CD4 afferent T suppressor cells are not natural killer T cells, but do express the CD25 cell surface marker.

Peripheral Tolerance Via the Anterior Chamber of the Eye: Role of B Cells in MHC Class I and II Antigen Presentation

“…These studies also demonstrated that antigenic moieties are released from F4/80 ϩ ocular APCs and captured via the BCR on the splenic B cells, internalized, and processed in acidified lysosomes before being presented to T cells (16). B cells are needed for the generation of both CD4 ϩ CD25 ϩ Tregs and CD8 ϩ Tregs in ACAID and for maintaining ocular immune privilege (13,15,17,18). The timehonored principle that Ag is presented to CD4 ϩ T cells via MHC class II (MHC-II) and that presentation to CD8 ϩ T cells occurs through MHC-I molecules led us to test the hypothesis that ACAID B cells present Ags on both MHC-I and MHC-II molecules during the establishment of peripheral tolerance.…”

“…An ear-swelling assay was used to measure DTH to either OVA or HEL as described previously (13). The results are expressed as follows: specific ear swelling ϭ (24 h measurement Ϫ 0 h measurement) for experimental ear Ϫ (24 h measurement Ϫ 0 h measurement) for negative control ear.…”

“…We used an in vitro spleen cell culture system that generates Tregs that express the same properties and surface markers as Tregs produced by AC injection (8,11,13,16,18,26). Moreover, the in vitro-generated T regs directly inhibit DTH and are Ag-specific CD8 ϩ T cells (16).…”

Emerging concepts in CD8+ T regulatory cells

“…Anterior chamber-associated immune deviation (ACAID) culminates in the appearance of CD8 + T regs that suppress Th1 immune responses, such as delayed-type hypersensitivity (DTH), and deviates antibody responses from complement-fixing isotypes to non-complement-fixing isotypes. F4/80 + ocular APC capture antigens introduced into the AC and then migrate to the spleen where they initiate a series of cellular interactions involving NKT cell emigrants from the thymus [12,13], B cells[5,6,14] CD4 + T cells [15,16], CD8 + T cells [17], and γδ T cells [18,19]. The process begins when ocular APC release antigenic fragments, which are captured by antigen-specific B cell receptors on splenic B cells.…”

CD4+CD25+Tregs express an increased LAG-3 and CTLA-4 in anterior chamber-associated immune deviation

“…CD4 + T suppressor cells from ACAID mice are able to transfer immune tolerance to naïve mice [21]. Further study proved that CD4 + T cells expressing CD25 and producing IL-10 are required for the development of ACAID [19]. CD4 +…”