Antigenic analysis of the IgA component of LDH-IgA immunoglobulin complexes

LDH-IgA complexes present in some human sera were purified by using affinity chromatography on 5'-AMP-Sepharose 4-B. The IgA component of the purified complexes was analysed in haemagglutination-inhibition tests. Antigenic determinants specific for alpha1 and alpha2 heavy chains and for kappa and lambda light chains were found. Earlier studies suggested that the IgA component is of kappa light chain type only. These different results are discussed. It is suggested that the LDH association site is located in the Fab fragment of the IgA component.