Delayed skin reactions were produced in rabbits with relatively low serum antibody titers by a single injection of a small amount of horseradish peroxidase (HRP) or of rat anti-HRP γ-globulin in complete Freund's adjuvant into the footpads. One to 2 days after skin testing, the reaction for the specific antibody was observed in the delayed skin lesions at the following locations: on the surface of lymphocytes and monocytes (macrophages); in the perinuclear region of small and medium sized lymphocytes; in blast cells; and in cytoplasmic granules of basophil leukocytes. The possible relationship of these antibody locations to delayed type or basophil cutaneous hypersensitivity was discussed. In mixed Arthus-type-delayed type hypersensitivity skin reactions to HRP in animals with high serum antibody titers, a different location of the antibody was observed. In confirmation of earlier data, the reaction occurred in cytoplasmic granules of macrophages and polymorphonuclear leukocytes and in association with collagen fibers, and antigen-antibody complexes accumulated especially in the walls and areas surrounding blood vessels. These localizations of the antibody were considered to be characteristic for Arthus-type hypersensitivity. When rabbits were double immunized against HRP and egg albumin, the reaction for (cytophilic) antibody to HRP on the surface of monocytes, lymphocytes and granulocytes in the upper dermis was as strong in the skin lesion elicited by egg albumin as in that elicited in the same animal by HRP. Lymphocytes with perinuclear antibody appeared in mixed Arthus-type-delayed type hypersensitivity skin reactions to HRP 1-2 days after skin testing but many plasma cells were seen only after 4-5 days in most cases. Observations are also reported on: the persistence of the antigens (HRP and rat anti-HRP γ-globulin) in the skin lesions; the acid phosphatase reaction in cells infiltrating the skin lesions; and cell contact, especially between lymphocytes and macrophages.
Delayed‐Type Hypersensitivity Skin Testing using Third Variable Loop Peptides Identifies T Lymphocyte Epitopes in Human Immunodeficiency Virus‐Infected Persons