Demonstration of B-cell maturation in X-linked immunodeficient mice by simultaneous three-colour immunofluorescence.

CBA/N mice carrying the X-linked immune deficiency gene (xid) have fewer splenic B cells than normal CBA mice and are unresponsive to a certain class of antigens. Studies of B-cell surface-marker expression and immune responsiveness have led to the commonly accepted idea that the B cells in adult xid mice are immature and resemble the B cells of young (1-3 week old) normal mice. That is, like young animals, xid mice lack cells in the most numerous of three IgM/IgD B-cell subpopulations (designated I in Fig. 1a, b) present in adult spleen. We now report, however, that this picture is an oversimplification and that in fact the B cells in adult xid mice differ from those present in either adult or young normal mice. Using quantitative three-colour fluorescence-activated cell sorter (FACS) analyses, we have compared the correlated expression of IgM, IgD and a newly discovered B-lymphocyte antigen (BLA-1) on splenic B cells in normal and xid mice. We show here (1) that most B cells in adult xid mice (as in normals) are BLA-1- whereas all B cells in young animals are BLA-1+; (2) that the major difference in the IgM/IgD B-cell subpopulations found between xid and normal mice is limited to the BLA-1- cells; and (3) that xid mice have increased numbers of BLA-1+ population III B cells.