Human autoantibody to vasoactive intestinal peptide: increased incidence in muscular exercise

Specific autoantibodies to vasoactive intestinal peptide were present in plasma from 29.6% healthy human subjects who habitually performed muscular exercise, compared to 2.3% healthy subjects who did not. Saturation analysis of VIP binding by the plasmas suggested the presence of 1 and 2 classes of autoantibodies in 5 and 3 high exercise subjects, respectively, distinguished by their equilibrium affinity constants (Ka). The mean Ka values for the high and low affinity autoantibody classes were, respectively, 1.3 x 10(8) M-1 and 0.8 x 10(7) M-1. These values are lower than the Ka range reported previously for tissue VIP receptors (G. Rosselin. Peptides 7, Suppl. 1, 89, 1986) but are larger than the inverse Michaelis constant (1/Km) for VIP-degrading proteases (T.N. Keltz, E. Straus, R.S. Yalow. Biochem. Biophys. Res. Commun. 92, 669, 1980). The autoantibodies may not interfere with VIP-receptor binding but are potential inhibitors of the proteolytic inactivation of VIP.