EVALUATION OF CANDIDATE INTERNATIONAL REFERENCE REAGENTS AND A MICRO-IMMUNODIFFUSION TEST FOR THE IDENTIFICATION OF PRECIPITINS TO THE H AND M ANTIGENS OF HISTOPLASMIN

Anti-Histoplasma capsulatum sera are specifically identified when they react with histoplasmin to form h and m precipitin lines in the agar-gel immunodiffusion test. Ten scientists from 9 nations evaluated candidate international reference sera and histoplasmin as international reference reagents for use in an agar-gel microimmunodiffusion test. Criteria for the acceptance of the test as an international reference method depended upon the determination of the sensitivity and specificity of the procedure when applied by each laboratory to 31 coded rabbit sera having diverse concentrations of antibody to the h or m antigens in the reference histoplasmin. Acceptance of a candidate lot of lyophilized histoplasmin and candidate reference antiserum was based upon the determination of the optimum reconstitution volumes of both reagents to give discrete and clearly delineated h and m precipitin lines identified by their position relative to the serum and antigen wells. The reagents were similarly tested by 5 laboratories using macroimmunodiffusion procedures. When the lyophilized histoplasmin was stored at 5.degree. C for 2 yr the h antigen showed no loss of relative potency; the m antigen showed a 20% loss. All of the 10 participating laboratories recommended that both the candidate serum and candidate histoplasmin be accepted as WHO International Reference Reagents for the identification of h and m precipitin lines. Eight of the 10 recommended that the described microimmunodiffusion test be accepted as the WHO Reference Method for the use of these reagents.