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Elicitation of Delayed Type Hypersensitivity in Chicks after In Ovo Sensitization with Different Molecular Forms of the Same Hapten

Lymphocyte sensitization, which participates in delayed type hypersensitivity (DTH) in chick embryos, was studied. The in ovo injection of dinitrophenylated keyhole limpet hemocyanine (DNP‐KLH) or DNP‐dextran (DNP‐D) led to delayed onset of the hapten‐specific reaction as shown by allergic contact dermatitis (ACD) after hatching. The extent of the ACD response was not directly dependent on the antigen dosage or the number of injections given for sensitizing. The magnitude of the ACD response was higher in chicks sensitized with DNP‐D than in those given DNP‐KLH. These findings suggest the presence of embryonic lymphocytes which can be sensitized by in ovo antigenic stimulation at the later stage of embryogenesis and may make possible the differentiation of functional lymphocytes. Antigen stimulation with higher doses may be inadequate for the in ovo sensitization of embryonic lymphocytes. The ACD response elicited by DNFB in chicks primed with either DNP‐KLH or DNP‐D was thought to be T‐cell dependent, from the kinetics of the ACD peak within a period of 24 to 48 hr. Furthermore the conditions for in ovo sensitization of embryonic lymphocytes by DNP‐D seem to be different from those for sensitization by DNP‐KLH.