Patients with lepromatous (low resistance) leprosy exhibit depressed cell-mediated immunologic reactivity. This is reflected by anergic responses to intradermal injection of various antigens, including lepromin, by relative inability to become sensitive to haptenes (dinitrochlorobenzene), and by poor blastogenic response of lymphocytes to various mitogens in cell culture. Patients with tuberculoid (high resistance) leprosy usually respond normally to these stimuli. Ability of lymphocytes to produce macrophage migration inhibition factor (MIF) has been shown to correlate with patient's ability to exhibit cell-mediated delayed-type hypersensitivity reactions. Lymphocytes of patients with lepromatous leprosy who are anergic fail to produce or produce only small amounts of MIF in response to lepromin in vitro, but lymphocytes of patients with tuberculoid leprosy who exhibit normal cell-mediated reactions respond to lepromin in vitro by production of greater amounts of MIF.
Katz SI, DeBetz BH, Zaias N. Production of Macrophage Inhibitory Factor by Patients With Leprosy. Arch Dermatol. 1971;103(4):358-361. doi:10.1001/archderm.1971.04000160008002