 The ability to respond to a polysaccharide vaccine antigen is an integral part of evaluating a patient with immunodeficiency. The pneumococcal vaccine Pneumovax remains the only readily available and the most widely used unconjugated polysaccharide vaccine. Although the pneumococcal vaccine is widely used test the immune systems response to a polysaccharide antigen, no clear guidelines or studies exist to what is considered a proper response to the Pneumovax . Immunoglobulin M IgM memory B cells are thought to play an important role in protection against pneumococcal disease. It is not known to what extent the ability of B cells to be activated in response to pneumococcal vaccination contributes to protective immunity. To address these issues, the following two specific aims are proposed: 