Immunoglobulin class specific antibodies to M. leprae in leprosy patients, including the indeterminate group and healthy contacts as a step in the development of methods for sero-diagnosis of leprosy

IgA, IgM and IgG anti-M. leprae antibody activity was quantitated by solid phase radioimmunoassay in groups of untreated leprosy patients throughout the spectrum, in lepromatous leprosy patients treated for more than 10 years, in an indeterminate leprosy group, and in a non-leprosy control group. IgA, IgM and IgG anti-M. leprae antibody activity increased from the group of healthy individuals exposed to M. leprae but without clinical signs of leprosy to tuberculoid (BT and BT/TT) and further to lepromatous (BL to LL) leprosy. There was a considerable overlap in IgA antibody activity, while the overlap between controls and tuberculoid and lepromatous leprosy was less than 20% in the IgM and IgG assays. After more than 10 years of treatment, the IgG anti-M. leprae activity had decreased markedly, whereas there was less effect in the IgA assay and no significant change in the IgM assay. In contrast to earlier findings, the group of 'strictly indeterminate leprosy' showed signs of an active humoral immune response against M. leprae. The IgM anti-M. leprae activity was higher in indeterminate leprosy than in the control group with virtually no overlap. IgA anti-M. leprae was higher in indeterminate leprosy, but with considerable overlap with the controls. No difference between these two groups was found in the IgG assay. The results are discussed in relation to the value of the various immunoglobulin specific anti-M. leprae assays for different purposes, including development of techniques for sero-diagnosis of leprosy.

Behavior of Mycobacterium leprae in human macrophages in vitro

Attempts have been made to cultivate Mycobacterium leprae in human macrophages in vitro. In 27 out of 55 experiments a two- to ninefold increase (mean 2.31 +/- 1.46) in acid-fast organisms were observed over a period of 1.5 to 3 months of cultivation. No such increase was observed with heat-killed bacilli (mean fold increase 0.88 +/- 0.19). Macrophages were necessary for obtaining increases. No multiplication was observed on artificial media. A close correlation between increases of acid-fast organisms and changes in viability as determined by the morphology of the bacilli (morphologic index) was found. The increases in acid-fast organisms could be inhibited by anti-leprosy drugs. It is concluded that multiplication of M. leprae may take place inside human macrophages in vitro. Multiplication appears not to be dependent on whether the macrophages are derived from lepromatous or tuberculoid patients or healthy individuals. Moreover, multiplication took place both at 33 and 37 C. The applicability of this method is at present limited by the restricted survival of human macrophages in vitro.

Immune responsiveness to Mycobacterium leprae and other mycobacterial antigens throughout the clinical and histopathological spectrum of leprosy

Immunological responsiveness was studied throughout the clinical and histopathological spectrum of leprosy (Ridley–Jopling scale) by the methods of lymphocyte transformation, leucocyte migration inhibition and delayed skin hypersensitivity,

The response to Mycobacterium leprae showed by all methods a continuous decrease from strong responses in the polar tuberculoid (TT) group to virtually negative responses in the polar lepromatous (LL) group. There was a good agreement between the in vitro methods and the lepromin skin test, giving support to the latter as useful tool in the evaluation of immune responsiveness to M. leprae in leprosy patients.

The immune response to BCG and PPD on the other hand, decreased only slightly towards the lepromatous pole of the spectrum, confirming the high degree of specificity of the immune defect in lepromatous leprosy. Patients grouped histologically as subpolar tuberculoid (TT/BT) reacted particularly strongly to BCG and PPD.

As it is likely that the methods used mainly measured T-lymphocyte function, the clinicopathological manifestations of leprosy appear to reflect the strength of the cellular immune response against M. leprae. Thus the findings give strong support to the concept of a host-determined, immunological diseases pectrum as expressed in the Ridley–Jopling classification.

Characterization of the cellular immune defect in lepromatous leprosy: a specific lack of circulating Mycobacterium leprae-reactive lymphocytes

The blastogenic response of leucocyte cultures from patients with tuberculoid and lepromatous leprosy has been studied. The leucocytes from the two groups were studied simultaneously and cultivated in the same pool of normal human serum. While the leucocytes from twenty-eight tuberculoid patients responded quite strongly to Mycobacterium leprae after 7 days of culture (average lymphocyte transformation 11·1%), there was a complete lack of response in similar cultures from twenty-seven lepromatous patients (average 0·1% transformed cells). These results were confirmed by studies on cellular incorporation of ³H-thymidine in the cultures from four tuberculoid and four lepromatous patients.

This lack of response was quite specific as leucocytes from several lepromatous patients responded to BCG. Furthermore, four patients with both lepromatous leprosy and tuberculosis responded as strongly to BCG and PPD as tuberculous patients without leprosy. In the mixed leucocyte reaction, between two lepromatous or two tuberculoid patients respectively, the lepromatous cells responded well (average 15·0%) and comparably to tuberculoid cells (average 12·1%).

The blastogenic response of purified lymphocytes to M. leprae revealed a similar pattern, i.e. the tuberculoid cells responded well, while again there was a lack of response in the lepromatous group.

It is concluded that the lepromatous patients lack circulating lymphocytes responding to M. leprae, indicating that their immunological defect as observed in the present study has features in common with immunological tolerance.