The ontogeny of cell‐mediated immunity: The response of the mouse to dinitrofluorobenzene (DNFB)

Cellular immunocompetence begins to develop in mice during the first week after birth, as indicated by skin allografting and graft‐versus‐host reactions, but delayed hypersensitivity has not yet been detected at this early age. The purpose of this study was to investigate the ontogeny of delayed hypersensitivity in suckling mice. Dinitrofluorobenzene (DNFB) is an antigenic hapten which, when applied to the skin, can elicit both delayed hypersensitivity and a humoral immune response. In adult mice the induction period of delayed hypersensitivity to DNFB is a blastogenic reaction (accumulation of lymphoblasts) in the diffuse, thymusdependent cortex of the lymph node draining the site of application. This blastogenic reaction reaches a peak three days after initial application of antigen and then subsides, to be followed by the development of germinal centers and numberous plasma cells — indicative of a humoral immune response — a week after initial sensitization. Suckling mice were sensitized by application of DNFB to the ears, and the auricular lymph nodes wer prepared for light and electron microscopy three and eight days after sensitization. The development of delayed hypersensitivity was assayed by applying DNFB to an ear, 5 to 12 days after initial sensitization, and measuring the increase in thickness of the ear 24 hours later. The results of these studies indicate that by two days of age, mice have the capacity to develop delayed hypersensitivity as shown by both a blastogenic reaction in the draining lymph node and a positive skin test. Mice sensitized at birth or on the next day did not respond in either way. Mice sensitized prior to two weeks of age did not develop the late phase of the response (the formation of germinal centers and plasma cells), which matured in parallel with the normal maturation of the machinery for antibody production during the third postnatal week. These observations strengthen the conclusion of previous investigations that the blastogenic response in the regional lymph node is the inductive phase of delayed hypersensitivity. Because the late phase of the response does not appear in mice sensitized before two weeks of age, these animals offer an unusual opportunity to study delayed hypersensitivity relatively uncomplicated by humoral antibody production.