Immunohistochemical characterization (original magnification × 20) of lymphocytes infiltrating the skin at sites of autologous Id challenge. A representative MM with a positive DTH reaction is shown. Formalin-fixed, paraffin-embedded skin biopsy sections were stained with the following antibodies: (A) polyclonal anti-CD3; (B) OPD4 MoAb (CD4/CD45R0); and (C) C8/144B MoAb (CD8).