ABSENCE OF IGD(-)CD27(-CELL POPULATION IN X-LINKED HYPER-IGM SYNDROME() MEMORY B)

The present study analyzed peripheral blood B cell populations separat ed by IgD and CD27 expression in six males with X-linked hyper-IgM syn drome (XHIM). Costimulation of mononuclear cells from most of the pati ents induced no to low levels of class switching from IgM to IgG and I gA with Staphylococcus aureus Cowan strain (SAC) plus IL-2 or anti-CD4 0 mAb (anti-CD40) plus IL-10. Measurable levels of IgE were secreted i n some of the patients after stimulation with anti-CD40 plus IL-4. Cos timulation with SAC plus IL-2 plus anti-CD40 plus IL-10 yielded secret ion of significant levels of IgG in addition to IgM, but not IgA. The most striking finding was that peripheral blood B cells from all of th e six patients were composed of only IgD(+) CD27(-) and IgD(+) CD27(+) B cells; IgD(-) CD27(+) memory B cells were greatly decreased. IgD(+) CD27(+) B cells from an XHIM patient produced IgM predominantly. Our data indicate that the low response of IgG production in XHIM patients is due to reduced numbers of IgD(-) CD27(+) memory B cells. However, the IgG production can be induced by stimulation of immunoglobulin rec eptors and CD40 in cooperation with such cytokines as IL-2 and IL-10 i n vitro.