Immunopathologic spectrum of leprosy. Immunopathologic spectrum of leprosy. Representative fields from each of the histopathological types of leprosy in the Ridley-Jopling classification are presented in the upper panel, in hematoxylin- and eosin-stained sections (magnification, ×63). The well-formed epithelioid granulomatous infiltrates seen in polar tuberculoid (TT) lesions become increasingly disorganized in each successive increment in the scale until they become completely disorganized aggregates of foamy histiocytes, with only occasional lymphocytes, in polar lepromatous (LL) lesions. Representative fields of each classification are shown in Fite-stained sections in the lower panel (magnification,× 1,000). A search of more than 50 fields was required to find the two organisms shown in a cutaneous nerve in the TT sample, and organisms are often similarly difficult to find in BT lesions. This spectrum is the yardstick against which is measured each new hypothesis and discovery regarding immunological mechanisms proposed to be responsible for the wide range of human responses to M. leprae. D. M. Scollard et al. Clin. Microbiol. Rev. 2006; doi:10.1128/CMR.19.2.338-381.2006