May stimulate primary immune response. Acts on T-cell stimulated sub-optimally through the TCR/CD3 complex stimulating their proliferation and cytokine production. Expressed in neutrophils. Isoforms 1 and 5 are expressed at high levels in the colon, lung,testis, lymph nodes and thyroid tissue. Isoform 5, but not isoform 1, is detected in spleen. Down-regulated in neutrophils after treatment with LPS and TNF. Belongs to the immunoglobulin superfamily. BTN/MOG family.