Inhibitory Effect of Heat-Labile Serum Factors on Detection of Staphylococcal, Pseudomonas, and Hepatitis B Surface Antigens by Solid-Phase Radioimmunoassay

Specific antibodies have previously been found to impair detection of staphylococcal antigen by solid-phase radioimmunoassay. The inhibitory effect of heat-labile serum factors on the detection of antigen is now described. Heating of serum at 56 C for 30 min prior to addition of antigens of Pseudomonas aeruginosa or Staphylococcus aureus improved sensitivity by eight- to 32-fold. Heating was less effective when performed after addition of antigen. Treatment with zymosan reduced the inhibitory effect of serum, although less effectively than did preheating. Antigen in buffer was detected with 16 times less sensitivity in antibody-coated tubes exposed to fresh serum than in tubes exposed to heated serum. These findings suggest that complement factors can interact with antibody in coated tubes and at least some antigens and thereby inhibit detection of antigen. The finding that heat treatment improved the sensitivity of Ausria II® -125 (Abbott Laboratories, North Chicago, Illinois) for hepatitis B surface antigen is of potential immediate clinical applicability.