– SECTM1A (secreted and transmembrane 1A), is 192 amino acid (aa) protein, appears to share structural and functional characteristics with other SECTM1 proteins. Human SECTM1 can be found either found as an approximately 27 kDa intracellular type I transmembrane protein that shows a perinuclear, Golgi like staining pattern, or as a 20 kDa soluble, secreted form, and is produced by some myeloid cells and by thymic epithelia and fibroblasts. Stimulation with IFN gamma is often necessary to detect human SECTM1 expression, and it is thought to be an interferon early response gene. Mouse SECTM1A cDNA encodes a signal sequence, an extracellular domain with four potential N linked glycosylation sites, a transmembrane sequence, and a very short (approximately 6 aa) cytoplasmic sequence. SECTM1 proteins from human and mouse show species specific binding of CD7 and co stimulation of T cells, including enhancement of CD3 induced proliferation.