The CD19/CD21 signal transduction complex of B lymphocytes

CD19 and CD21 are B-cell surface molecules that associate with each other and with CD81 and Leu-13 to generate a signal transduction complex that is independent of the antigen receptor. Current studies, reviewed here by Thomas Tedder, Liang-Ji Zhou and Pablo Engel, indicate an important biological role for this protein complex in the regulation of B-cell development and activation.