WHY RELAPSE OCCURS IN PB LEPROSY PATIENTS AFTER ADEQUATE MDT DESPITE THEY ARE MITSUDA REACTIVE - LESSONS FROM CONVITS EXPERIMENT ON BACTERIA-CLEARING CAPACITY OF LEPROMIN-INDUCED GRANULOMA

It is amazing how after years of scientific research and therapeutic p rogress many simple and basic questions about protective immunity agai nst Mycobacterium leprae remain unanswered. Although the World Health Organization (WHO) has recommended short-term multidrug therapy (WHO/M DT) for the treatment of paucibacillary (PB) leprosy patients, from ti me to time several workers from different parts of the globe have repo rted inadequate clinical responses in a few tuberculoid and indetermin ate leprosy patients following adequate WHO/MDT despite the fact that they are Mitsuda responsive. A few borderline tuberculoid patients har bor acid-fast bacilli (AFB) in their nerves for many years even though they become clinically inactive following MDT a fact which has been i gnored by many leprosy field workers. Keeping these patients in mind, we have attempted to investigate the cause of the persistence of AFB i n PB cases and have looked into the question of why Mitsuda positivity in tuberculoid and indeterminate leprosy patients, as well as in heal thy contacts, is not invariably a guarantee for protectivity against t he leprosy bacilli. We have: a) analyzed the histological features of lepromin-induced granulomas, b) studied the bacteria-clearing capacity of the macrophages within such granulomas, and c) studied the in vitr o leukocyte migration inhibition factor released by the blood leukocyt es of these subjects when M. leprae sonicates have been used as an eli citor. The results of these three tests in the three groups of subject s have been compared and led us to conclude that the bacteria-clearing capacity of the macrophages within lepromin-induced granuloma (positi ve CCB test) may be taken as an indicator of the capability of elimina tion of leprosy bacilli and protective immunity against the disease. T his important macrophage function is not invariably present in all tub erculoid and indeterminate leprosy patients or in all contacts even th ough they are Mitsuda responsive and are able to show a positive leuko cyte migration inhibition (LMI) test. It is likely but not certain tha t this deficit of the macrophage is genetically predetermined and pers ists after completion of short-term WHO/MDT. Thus, after discontinuati on of treatment slow-growing, persisting M. leprae multiply within mac rophages leading to relapse.