THE ROLE OF PROTEIN-TYROSINE PHOSPHATASES IN LYMPHOCYTE-ACTIVATION AND DIFFERENTIATION

Protein tyrosine phosphorylation is involved in the regulation of ever y facet of biological phenomena. Signal transduction mechanisms operat ive in lymphocyte development, activation, and differentiation have be en studied intensively, and are also found to support this premise. In this review, I focus on the crucial problems surrounding CD45, a prot otypic receptor-type protein tyrosine phosphatase (RPTP) of the immune system: (1) the role of CD45 for antigen receptor-initiated signaling in T and B cells, (2) the physiological relevance of CD45 isoforms, ( 3) potential regulatory mechanisms of CD45 PTP activity, and (4) the c linical significance of structural abnormalities in PTP. Furthermore, other PTPs that may be important to the exquisite functioning of the i mmune system are reviewed.