Cuta neous basophil responses in neonatal guinea pigs: active immunization, hapten specific transfer with small amounts of serum, and preferential elicitation with phytohemagglutinin skin testing.

Previous studies have demonstrated a failure to elicit delayed hypersensitivity skin responses in neonatal guinea pigs despite apparent immunologic competence of their lymphocytes and monocytes. The ability of neonatal guinea pigs to manifest cutaneous basophil hypersensitivity (CBH) responses was examined. Neonates were competent to express macroscopic and microscopic aspects of these delayed reactions. Strong cutaneous basophil responses were elicited in newborns (0 to 2 days old) in a hapten-specific manner after intravenous transfer of small amounts of immune serum (0.5 ml) obtained from adult donors. Also, neonatal guinea pigs actively immunized at birth with hapten-carrier conjugates emulsified with incomplete Freund's adjuvant (IFA) and skin tested when 1 week old had 24-hr hapten-specific cutaneous basophil reactions and CBH reactions to the carrier protein as well. Compared with adult CBH reactions, neonatal responses had equal concentrations of basophils, fewer monocuclear cells, less macroscopic erythema, and almost no induration. Hapten-specific CBH reactions also contained significant infiltrates of eosinophils which were more prominent in the ear skin vs flank skin and in neonates vs adults. Immunization with complete Freund's adjuvant (CFA) resulted in a marked difference between adults and neonates; adult PPD reactions were quite indurated and contained many more monoculear cells and few basophils, whereas neonatal PPD reactions were flat, erythematous, nonindurated, and contained relatively few mononuclear cells and more basophils. Thus, neonatal tuberculin reactions elicited by PPD in animals immunized with CFA were examples of CBH. Skin testing nonimmune guinea pigs with phytohemagglutinin (PHA) also revealed marked differences in 24-hr cutaneous reactions between adults and newborns. Adults had indurated and erythematous reactions which contained approximately 20% basophils and 80% mononuclear cells, whereas similar PHA skin tests in newborns elicited small macroscopic reactions, which microscopically showed large infiltrates containing approximately 80% basophils and 20% mononuclear cells. It was concluded that neonatal guinea pigs were not only competent to manifest basophil-containig delayed-type reactions, but that cutaneous basophil responses were preferentially elicited in these animals under a variety of circumstances. These results underline the fact that basophil accumulations are one aspect of delayed skin test responses and that the regulation of the arrival of these cells in neonates is different from that in adult guinea pigs.