APS (adapter molecule containing PH and SH2 domains), SH2-B and Lnk compose a family of adapter proteins, which contain a pleckstrin homology (PH) domain, an SH2 domain and a tyrosine phosphorylation site. Stimulation of B cell receptor (BCR) or T cell receptor (TCR) results in the phosphorylation of the immunoreceptor tyrosine-based activation motif (ITAM) of BCR, TCR and several substrates. APS, SH2-B and Lnk may bind to the ITAM domain of BCR and TCR. Lnk is tyrosine phosphorylated in response to TCR stimulation and APS has been shown to be tyrosine phosphorylated in response to BCR stimulation.