Absence from sera from normal individuals or from rifampin-treated leprosy patients (THELEP trials) of antibody to rifamycin-protein or rifamycin-membrane conjugates.

It has been reported that normal individuals have precipitating antibody which binds to rifamycin-conjugated proteins. An enzyme-linked immunosorbent assay has failed to confirm this claim, although antibodies demonstrable in a solid-phase binding assay are easily raised in mice if complete adjuvant is used. Moreover, no antibodies to rifamycin-protein conjugates were found in sera from the patients included in THELEP trials of six rifampin-containing regimens. Similarly, there was no antibody by the indirect Coombs test performed in another laboratory. Further studies using rifamycin-membrane conjugates regarded as more likely to be immunogenic in vivo also failed to reveal antibody in patients' sera, although this technique revealed an interesting antibody in one of four control sera known to be positive by the indirect Coombs test.