Evaluation of cell mediated immunity in healthy contacts of leprosy

The cell mediated immunity (CMI) was studied in 50 healthy contacts of leprosy patients and 50 age & sex matched non-contact controls by lepromin test and leucocyte migration inhibition (LMI) test using phytohaemagglutinin (PHA) and lepromin and its association with other risk factors in contacts was assessed. The lepromin positivity correlated well with LMI results. There was no difference in CMI in I, II and III degree of contacts. Amongst direct contacts lepromin test was positive in 67 per cent as compared to 92 per cent in indirect contacts while in LMIT migration index (MI) was significantly increased (0.66 +/- 0.20) in direct contacts. MI was also significantly increased (0.73 +/- 0.20) contacts of less than two years duration which decreased to 0.51 +/- 0.18 in contacts of more than five years duration. Lepromin positivity also increased from 60 per cent to 100 per cent in these contacts. The specific CMI was significantly suppressed in contacts of LL patients (MI:0.74 +/- 0.21) and BL patients (MI: 0.61 +/- 0.01) as compared to healthy controls. B.C.G. vaccinated individuals showed better CMI response. The findings in the study showed specific unresponsiveness to lepromin in LMI in leprosy contacts of less than two years duration, direct contacts, contacts of lepromatous spectrum of index patients and contacts not vaccinated with B.C.G. emphasizing that CMI status is an important parameter in identifying the contact population at the greater risk of acquiring leprosy.