Macrophages regulate induction of delayed‐type hypersensitivity and experimental allergic encephalomyelitis in SJL mice

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Abstract
The relationship between the delayed‐type hypersensitivity (DTH) response and susceptibility to experimental allergic encephalomyelitis (EAE) was examined using a unique age‐dependent defect in the DTH response in an EAE‐susceptible mouse strain. Young adult male SJL mice (< 10 weeks of age) are defective in DTH responses following immunization with a variety of soluble antigens. By contrast, they respond to antigens applied to the skin, demonstrating a normal contact sensitivity response. In this report, we show that the nonresponder male SJL are also unable to mount a DTH response to soluble neuroantigens or neuroantigens emulsified in complete adjuvant, and are additionally resistant to actively induced EAE. This contrasts with the DTH response in older males (> 10 weeks of age) and young adult females (6 weeks of age), which are both DTH responders and susceptible to EAE. By contrast, all three groups are susceptible to EAE mediated by the transfer of activated effector T cells, suggesting that the defect in young adult males is in the induction of effectors. Furthermore, transfer of a macrophage population from female responders to young male non‐responders mediates the induction of both DTH responsiveness and EAE susceptibility. The phenotype of this antigen‐presenting cell is (I‐A+, Mac‐1+, Mac‐2−, Mac‐3+), identical to the phenotype of the macrophage regulating DTH responsiveness in this strain of mice. These data are consistent with the hypothesis that a defect in this cell inhibits induction of both CD4+ Th1 DTH and EAE effector T cells.