HS1 is dispensable for PLCγ1 phosphorylation and recruitment to the IS. A, T cells from HS1+/+ or HS1−/− mice were stimulated as indicated, and lysates were analyzed by Western blotting for PLCγ1 phosphorylated at Y783, total PLCγ1, and HS1. B, CD4+ T cells from HS1+/− or HS1−/− AND TCR transgenic mice were conjugated to CMAC-stained, MCC peptide-loaded CH27 B cells (blue) and stained for PLCγ1 (red). C, Conjugates prepared as in B were scored for recruitment of PLCγ1 to the cell-cell contact site.