T cell-independent B cell memory.

Despite being unable to mount a bona fide recall antibody (Ab) response to secondary immunization, T cell-independent antigens (TI Ag) such as pneumococcal capsular polysaccharides (PS) can generate protective humoral immunity in adults. The concept of TI B cell memory after being iconoclastic for decades has now received experimental support from several laboratories. TI B cell memory comprises two components: i) memory B lymphocytes that differ phenotypically and functionally from their T cell-dependent counterparts, ii) memory bone marrow plasma cells that play a crucial role in the immune protection conferred by TI polysaccharidic vaccines. B-1b cells constitute the major source of both TI memory lymphocytes and plasma cells. This conceptual shift should lead to rehabilitate the TI arm of the immune system for vaccination purposes.