Coccidioides immitis spherule

Delayed type hypersensitivity reaction begin with the C.immitis antigen is presented to CD4 and CD8 lymphocytes by antigen presenting cells. This causes the secretion of interleukins and other lymphokines from macrophage cells. The release of effector molecules causes blood vessels to become permeable and allows fibrinogen to escape into the surrounding tissue where it is converted to fibrin. The deposition of fibrin and the movement of T-cells and monocytes in the extracellular spaces cause the tissue to become indurated. The induration is usually detectable in 18 hours and peaks at 48 hours.