Suppression of the cellular interactions of delayed hypersensitivity by corticosteroid.

Methylprednisolone sodium succinate was administered to New Zealand white rabbits sensitized with BCG in an attempt to define the effect of corticosteroid upon the interactions of lymphocytes and macrophages in the afferent and efferent limbs of delayed hypersensitivity. Daily intramuscular administration of the corticosteroid, beginning simultaneous with BCG sensitization of rabbits, prevented the inhibition of macrophage migration following tuberculin challenge 14 days after sensitization. If corticosteroid administration was delayed until 10 days following sensitization with BCG, the expected inhibition of macrophage migrations followed tuberculin challenge. Purified lymphocytes obtained from sensitized rabbits not treated with corticosteroid, when added to cells isolated from rabbits treated with methylprednisolone from the time of sensitization, re-established the expected inhibition of macrophage migration. In contrast purified lymphocytes obtained from animals treated with corticosteroid from the time of BCG sensitization did not elaborate a factor which inhibited macrophage migration. Excluding direct effects upon blood vessels, these observations suggest that the afferent rather than the efferent stage of delayed hypersensitivity is suppressed by corticosteroid.