Membrane-spanning four-domains subfamily A (MS4A) includes B-cell-specific antigen CD20 (MS4A1), high affinity immunoglobulin epsilon receptor beta chain (MS4A2), hematopoietic-cell-specific protein HTm4 (MS4A3), and related proteins. These proteins share a similar structure with four transmembrane domains and have amino acid identities of 25-40% []. They are predominantly expressed in hematopoietic cells, but some can be found in other tissues including testis and brain [, ].MS4A1 (B-lymphocyte antigen CD20) [], MS4A2 (high affinity IgE receptor subunit beta) [, ], and MS4A4B []have been shown to have an important role in immunity.Several variants within the MS4A gene cluster have been implicated in Alzheimer's disease [].
