Discovering how DO regulates lymphocyte function

Abstract

HLA-DO or H-2O (DO) in mice is a non-classical, non-polymorphic MHC II molecule primarily expressed in the thymic medulla and B cells. While the common belief is that DO inhibits the activity of DM, controversial data opposes that point of view. Applying physicochemical studies to purified DO, DM, and HLA-DR1, we have demonstrated that DO interacts directly with HLA-DR1 molecules in a peptide-receptive-conformation, augmenting binding of ‘DM-resistant’ peptides, while inhibiting binding of ‘DM-sensitive’ peptides to HLA-DR1. Indeed, we have observed that DO-WT B cells express higher densities of pMHC from naturally processed protein antigens in vivo. Accordingly, DO-KO mice are more susceptible to development of EAE due to presence of larger numbers MOG/IAb-specific CD4 T cells in periphery, likely due to a less effective thymic deletion. Since DO is also expressed in B cells, and B cell antigen presentation is a critical step in differentiation of CD4 memory T cells, we tested the contributions of DO to the development of CD4 memory T cells. To do so, we used DR1+/DO-KO mice, and examined CD4 memory development to DR1 restricted flu specific T cells three months post flu vaccine immunization. We found that consistent with our hypothesis, the DR1+/DO-KO mice had fewer flu specific CD4 memory T cells than DR1+/DO-WT mice. By in vitro and in vivo recall experiments, we also found that the secondary immunological responses in DR1+/DO-KO mice were compromised. In addition, we recovered fewer memory B cells from immunized DR1+/DO-KO mice. These results demonstrate that in the absence of DO, the presentation of cognate foreign antigens in the DO-KO mice is altered and can potentially hamper the proper development of memory cells after the resolution of the infection. These findings support the idea that the expression of DO might ensure the proper development of memory cells.