MHC Class II Expression in Double Mutant Mice Lacking Invariant Chain and DM Functions

Abstract

Invariant (Ii) chain and DM functions are required at distinct stages during class II maturation to promote occupancy by diverse peptide ligands. The class II molecules expressed by mutant mouse strains lacking Ii chain or DM activities display discrete structural and functional abnormalities. The present report describes the cellular and biochemical characteristics of Ii−DM− doubly deficient mice. As for Ii chain mutants, their mature AαbAβb dimers similarly exhibit reduced mobilities in SDS-PAGE, and in functional assays these molecules behave as if empty or occupied by an easily displaced peptide. Additionally, the present experiments demonstrate that the production of floppy AαbAβb dimers is TAP independent. In comparison with Ii chain mutants, Ii−DM− doubly deficient cell populations exhibit increased peptide binding activities and consistently greater presentation abilities in T cell stimulation assays. These functional differences appear to reflect higher class II surface expression associated with their increased representation of B lymphocytes. We also observe defective B cell maturation in mice lacking Ii chain or DM expression, and interestingly, B cell development appears more severely compromised in Ii−DM− double mutants. These mutant mice lacking both Ii chain and DM activities should prove useful for analyzing nonconventional class II Ag presentation under normal physiological conditions in the intact animal.

Presenting Exogenous Antigen to T Cells

“…In analysis of the class II MHC pathway, human HLA‐DM‐deficient cell lines are available (Riberdy et al, ; Denzin et al, ; Fling et al, ; Morris et al, ). The knockout mice lacking expression of H2‐DM and/or invariant chain have been characterized (Fung‐Leung et al, ; Martin et al, ; Miyazaki et al, ; Tourne et al, ; Kenty et al, ). Although transformed cell lines that are deficient in H2‐DM (the murine homolog of HLA‐DM) are less available than human HLA‐DM‐deficient cell lines, murine class II MHC molecules can function with HLA‐DM, allowing the analysis of the dependence of murine class II MHC molecules on HLA‐DM function (as a surrogate for H‐2M function) by the use of HLA‐DM‐deficient human cell lines that have been transfected to express murine class II MHC molecules (Brooks et al, ; Diment and Shinde, ; Stebbins et al, ).…”

“…cell lines are available (Riberdy et al, 1992;Denzin et al, 1994;Fling et al, 1994;Morris et al, 1994). The knockout mice lacking expression of H2-DM and/or invariant chain have been characterized (Fung-Leung et al, 1996;Martin et al, 1996;Miyazaki et al, 1996;Tourne et al, 1997;Kenty et al, 1998).…”