The Complexity of the HL‐A Gene Product I: Study of a Serum Produced Against HL‐A5 in an HL‐A Semi‐Identical Situation

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Abstract
A complex antibody developed in a W18 father immunized by his HL–A5 daughter was analysed. Four different antibodies appeared successively and were isolated by absorption and elution. These antibodies react directly or indirectly (CYNAP) with HL‐A5, W21, W5, W17 and W15 cells. Some W21 cells are not reactive (ET*); some W5 cells are directly reactive, others only in CYNAP, which enables these two categories of cells to be subdivided.By absorption‐inhibition, it was possible to demonstrate the existence of several determinants on the gene product, since the saturation of the absorbing cells by one antibody does not prevent the absorption of a second antibody (anti‐HL‐A5 and anti‐[5, W21, W5]). These distinct determinants or antigenic factors (Dausset et al. 1965) are shared by several allelic products. Their structures are probably similar since they are cross‐reactive. Capping experiments indicate that all these determinants are borne by the same second locus molecule and are independent of the third locus molecule.The hypothesis that these shared and cross‐reactive antigenic factors derived from each other by successive duplication and mutation of the corresponding gene is again emphasized.