IMMUNE RESPONSES OF HUMAN ADULTS AFTER ORAL AND PARENTERAL EXPOSURE TO BOVINE SERUM ALBUMIN

Investigations were carried out to examine the possible causes of the low incidence and low levels of anti-BSA in human adults as compared to those of normal children. To determine if the reduced amount of BSA in the adult diet was an important factor, childhood levels of dietary BSA in the form of oral supplemental doses were administered to 17 normal human volunteers for 21 days. To learn if the manner in which dietary protein was catabolized by the gastrointestinal tract of the adult was a determining factor, selected individuals were also stimulated by intradermal injections of BSA. When anti-BSA was present before the experiment, there was a measureable antibody response following both methods of stimulation. The responsiveness of this group indicates that, among adults who retained the capacity to produce anti-BSA, the dose of antigen was an important variable in determining the amount of antibody actually produced. When no anti-BSA or very low levels existed before the experiment, the adults were unresponsive or hyporesponsive to both methods of stimulation. At least 80 per cent of these unresponsive adults had been synthesizing anti-BSA during childhood and should have resumed antibody production had their adult unresponsiveness been due to either a low dietary intake of BSA or the gastrointestinal conditions unique to adults. Circulating antigen was demonstrated in the sera of individuals without anti-BSA for as long as 21 days after intradermal injections of BSA. In subjects with trace amounts of anti-BSA prior to the intradermal injection of BSA, both BSA and anti-BSA were demonstrated to exist simultaneously in the serum for a minimum of 21 days. These data suggest that antigenantibody complexes can sometimes persist in the circulation for prolonged periods following the injection of relatively small doses of antigen into human subjects. None of the subjects demonstrated an immediate wheal-and-flare response, an Arthus reaction, or a tuberculin type of response when tested either before or after the experiment. Thus it appears that the low incidence of detectable anti-BSA among adults is due in part to an acquired immunological hyporesponsive state to BSA. © 1968.