Activation of Src-family kinases leads to both stimulatory and inhibitory signaling responses, with cell-specific and signaling pathway-specific outcomes and redundancy of kinase function.

Immune system:
In immune cells Src kinases are involved in many signalling pathways, including ITAM- and ITIM-domain-containing receptor signaling, integrin signaling, and responses to chemokines/chemoattractants, cytokines, innate immune stimuli and a large variety of non-immune cell specific stimuli (UV irradiation, heat, osmotic shock etc.). In many cases Src kinases signal to MAP kinase or NF-κB pathways, but they can also modulate other pathways through less well characterized mechanisms.

The primary T cell Src kinases are Lck and Fyn; the main B cell Srcs are Lyn, Fyn and Blk. Mast cells express Fyn and Lyn, with low expression of Src.