Analysis of VH and VL genes of a monospecific human anti-myosin antibody produced by a B cell from the primary repertoire.

Epstein-Barr virus (EBV) transformation of B lymphocytes from a Glanzmann's thrombasthenia patient with a serum antibody to the integrin alpha IIb beta 3, led to the immortalization of a B cell secreting a monospecific IgM monochonal antibody (MAb), B7, reactive with platelet myosin. Analysis of B7 V genes revealed minimally mutated sequences: the immortalized B cell issued from the primary repertoire, with no evidence of an in vivo selection by myosin. The V genes were here compared with sequences of human MAbs available on databases to more clearly understand the monospecificity of the B7 MAb. B7 V genes were closely identical to rearranged V genes in clones with self-specificities, often secreting polyreactive antibodies. In contrast, B7 is an unmutated monoreactive human MAb able to recognize myosin with a high avidity. Comparison of the CDR3H sequence with that of MAbs in databases supports a central role for the CDR3H subdomain in determining monospecificity. Our results suggest the existence of a monospecific autoreactive B cell compartment, besides the well-known polyspecific one, susceptible to be the template of pathogenic autoreactivity, characterized by antibodies of high affinity and specificity.