title: The origin of the immune system. The possibility that immunoglobulin superfamily molecules and cell adhesion molecules of chicken and slime mould are all related.
abstract: It has been suggested that the neural cell adhesion molecules (N-CAM) are members of the Ig superfamily. We have examined structural homology between the N-CAM and other superfamily molecules in detail. The Ig-like domains of N-CAM have overall sizes similar to those of Ig constant domains or major histocompatibility complex (MHC) domains. Significant sequence homology was found between the N-CAM Ig-like domains and several other Ig superfamily members, such as T4, T8, IgA transport receptor, Ig VH, Ig C mu 4, and others. A comparison of the second domain of T4 (255 amino acids) with the central domain of N-CAM (302 amino acids) has demonstrated a significant sequence homology. Furthermore, a cell adhesion protein, cs-A, of slime mould, Dictyostelium, also seems to be related to N-CAM. It appears that the Ig superfamily of the immune system originated from more ubiquitous cell recognition molecules which are common in all metazoan species.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000954:Antigens, Surface / Q000235:genetics*; D005075:Biological Evolution; D015815:Cell Adhesion Molecules; D002645:Chickens; D004023:Dictyostelium; D007136:Immunoglobulins / Q000235:genetics*; D005810:Multigene Family; D011487:Protein Conformation; D011948:Receptors, Antigen, T-Cell / Q000235:genetics*
chemical_list: D000954:Antigens, Surface; D015815:Cell Adhesion Molecules; D007136:Immunoglobulins; D011948:Receptors, Antigen, T-Cell