Three dimensional structure of a natural auto antibody — A predicted model of the antigen binding site

In the complex network of the immune system, antibodies play a major role in binding antigen, thereby activating the immune humoral response and aiding in elimination of the foreign particle. There are millions of antibodies in the body ready to encounter the myriad of different antigens. Only when a proper fit occurs between the antibody and the antigen, a strong immune response is elicited and the body gets rid of the antigen. Unfortunately, by some unknown mechanism autoantibodies are also produced in the body of some individuals. These autoantibodies bind specifically to self-antigens, thus leading to an unfavorable pathogenic situation of autoimmunity. In addition, natural autoantibodies are produced by a subset of B cells (B-l) which are polyreactive and may bind several self antigens. In this paper, we modeled the 3-D structure of a natural autoantibody whose deduced amino acid sequence is known. This antibody was produced by malignant, hyperdiploid B-l clones. We compared the antigen binding site (Fab) of this natural autoantibody to a normal antibody and found that the tertiary structure of this autoantibody resulted in an antibody(Ig) with a shallow binding groove relative to the original antibody. It is possible that alterations in the binding groove are responsible for polyreactivity.