MHC class I phenotype and function of human beta 2-microglobulin transgenic murine lymphocytes

Lymphoid cells from beta(2)-microglobulin (beta(2)m) knockout mice transgenic for human (h) beta(2)m (C57BL/10 m beta(2)m(-)/h beta(2)m(+)) were compared with normal mice for their binding to exogenously added h beta(2)m, binding to a H-2D(b) peptide and for functional activity in a one-way allogenic MLC. Based on data from cellular binding studies, Scatchard analyses and flow cytometry, it is concluded that exogenous h beta(2)m does not bind to hybrid MHC class I (MHC-I) molecules composed of mouse heavy chain/h beta(2)m molecules expressed on lymphocytes of transgenic mice. Immunoprecipitation and SDS-PAGE analysis of metabolically labelled normal C57BL/6 lymph node cells showed binding of exogenous h beta(2)m to MHC-I, in particular, to the H-2D(b) molecule through an exchange with endogenous mouse beta(2)m. In contrast to normal H-2D(b) molecules, hybrid H-2D(b) expressed on the surface of transgenic lymphocytes binds radiolabelled peptide in the absence of exogenous added h beta(2)m suggesting that a stable fraction of hybrid H-2D(b) molecules is empty or contain peptides with very low affinity. In a one-way allogenic mixed lymphocyte culture, transgenic splenocytes were found to be far less stimulatory than normal splenocytes. In contrast, transgenic alloreactive cytotoxic T lymphocytes developed earlier in MLC than their non-transgenic counterparts. These data indicate that the hybrid mouse heavy chain/h beta(2)m complex alters the alloantigenic repertoire and influences important aspects of T-cell activation.