SOCS4 and SOCS5
In contrast to SOCS1, 2 & 3, we still know very little about the physiological role of either SOCS4 or SOCS5.
The CD4+ Th2-derived cytokines such as IL-4 coordinate immune responses to parasitic infections and when inappropriately activated contribute to the pathogenesis of allergic inflammatory diseases such as asthma. SOCS5 expression is increased in macrophages in response to IL-4 and when over-expressed, SOCS5 can inhibit IL-4 signalling.
However, in SOCS5-deficient mice, Th1/Th2 cells differentiate normally, the mice mount normal B and T cell responses to mitogenic stimuli and macrophages derived from the mice respond normally to IL-4. Our laboratory is interested in solving this apparent paradox.
Despite a high degree of amino acid identity within the SOCS4 and SOCS5 SH2 domains, the two proteins appear to have quite distinct activities. We remain interested in finding a functional role for SOCS4.