Original antigenic sin at the cellular level I. Antibodies produced by individual cells against cross‐reacting haptens

Abstract “Original antigenic sin” has been studied in the mouse at the cellular level using two cross‐reacting haptens: m‐aminobenzoic acid (mB) and m‐sulfanilic acid (mS). The number of antibody‐forming cells (AFC) was measured by the local hemolysis technique using red blood cells coupled to the haptens. Immunization was performed with the haptens coupled to a carrier protein (human γ‐globulin) in Freund's adjuvant. It was found that a heterologous booster was always followed by an increase of the AFC specific of the primary antigen, larger than what could be expected from the cross‐reactivity of the two haptens. In the case of primary stimulation by mS and secondary stimulation by mB, it was observed that the absolute number of AFC against mS was greater than the AFC against mB.