Studies on non-H-2-linked lymphocyte-activating determinants. II. Nonexpression of Mls determinants in a mouse strain...

Minor lymphocyte-stilulating (MIs) coded non-H-2-linked lymphocyte-activating determinants (LADs) are present on a late developing subpopulation of murine B lymphocytes. Spleen cells derived from CBA/N mice, a strain with an X-linked defect in B cell function, failed to stimulate a response in MIs-defined mixed lymphocyte reactions (MLRs) with H-2 identical CBA/J or C3H/N responder spleen cells. However, both CBA/J and C3H/N spleen cells induced significant responses in CBA/N responder spleen cells. The inability of CBA/N cells to induce an MIs-defined response was not due to the presence of the nonstimulatory MIsb genotype, since spleen cells of immunologically normal F1 mice derived from crosses of CBA/N and C3H/N mice were stimulatory in MLRs for C3H/N responder cells. Immunologically abnormal CBA/N female x C3H/N male) F1 male mice, which are hemizygous for the CBA/N X chromosome, were also unable to induce a response in MIs-defined MLRs. Although the MIs coded LADs are not X linked in immunologically normal mouse strains, these data indicate that the failure of CBA/N mice to functionally express the MIs-coded LADs is X linked. This characteristic was not secondary to the presence of suppressor cells and is most likely related to the absence of a late developing (mature) subpopulation of B lymphocytes in these mice.