Immunology of reactions in leprosy. Current status

Time to revisit the purported link of leprosy reactions with infective triggers: An unnecessary economic burden for patients

Existing literature on factors triggering leprosy reactions is based only on case reports and case series, and thus probably gives a biased view. We undertook a case-control study to investigate such purported trigger factors in 42 leprosy reaction patients and 40 non-reactional controls, and the cost of investigations required for the same. Detailed history, clinical evaluation and investigations for triggers were carried out. Infections (typhoid, dental caries) were the most common triggers found, followed by pregnancy. Trigger factors were commoner in the type 2 reaction (T2R) group compared to type 1 (T1R) reaction group. There was however no statistical difference between the two groups. The average estimated cost of investigations was higher in the reactional group and this difference was statistically significant. Hence, except for essential investigations required for initiating steroids, an extensive battery of investigations is unjustified unless the medical history suggests a definitive infective trigger.

Mycobacterium leprae actively modulates the cytokine response in naive human monocytes

Leprosy is a chronic but treatable infectious disease caused by the intracellular pathogen Mycobacterium leprae. Host immunity to M. leprae determines the diversity of clinical manifestations seen in patients, from tuberculoid leprosy with robust production of Th1-type cytokines to lepromatous disease, characterized by elevated levels of Th2-type cytokines and a suboptimal proinflammatory response. Previous reports have indicated that M. leprae is a poor activator of macrophages and dendritic cells in vitro. To understand whether M. leprae fails to elicit an optimal Th1 immune response or actively interferes with its induction, we have examined the early interactions between M. leprae and monocytes from healthy human donors. We found that, in naïve monocytes, M. leprae induced high levels of the negative regulatory molecules MCP-1 and interleukin-1 (IL-1) receptor antagonist (IL-1Ra), while suppressing IL-6 production through phosphoinositide-3 kinase (PI3K)-dependent mechanisms. In addition, low levels of proinflammatory cytokines were observed in association with reduced activation of nuclear factor-kappaB (NF-kappaB) and delayed activation of IL-1beta-converting enzyme, ICE (caspase-1), in monocytes stimulated with M. leprae compared with Mycobacterium bovis BCG stimulation. Interestingly, although in itself a weak stimulator of cytokines, M. leprae primed the cells for increased production of tumor necrosis factor alpha and IL-10 in response to a strongly inducing secondary stimulus. Taken together, our results suggest that M. leprae plays an active role to control the release of cytokines from monocytes by providing both positive and negative regulatory signals via multiple signaling pathways involving PI3K, NF-kappaB, and caspase-1.

Erythema Nodosum Leprosum: Reactional Leprosy

The different clinical forms of leprosy are mainly related to the variety of immunological responses to the infection. Thus, lepromatous leprosy occurs in patients with a poor cell-mediated immunity to Mycobacterium leprae, whereas tuberculoid leprosy is associated with a high resistance to leprosy bacillus. Intermediate forms, including borderline tuberculoid leprosy, borderline lepromatous leprosy, and borderline leprosy, are a continuous and unstable spectrum of the disease. Leprosy reactions are rare and not well-known states that interrupt the usual chronic course and clinical stability of patients with leprosy. They are expressions of immunological perturbations. Attending to the clinical and histopathological manifestations, leprosy reactions may be separated in 2 or 3 different variants: reverse reaction (type I), erythema nodosum leprosum (type II), erythema polymorphous (type II) and Lucio's phenomenon, mainly considered a type II reaction, but sometimes designated type III. Type I leprosy reaction, also named "upgrading reaction," occurs in borderline leprosy states and is associated with a shift toward the tuberculoid pole. Type II reaction usually occurs in lepromatous leprosy, and there are 3 different clinical variants, including erythema nudosum leprosum, erythema polymorphous-like reaction, and Lucio's phenomenon.

The expression of NGFr and PGP 9.5 in leprosy reactional cutaneous lesions: an assessment of the nerve fiber status using immunostaining

The effects of reactional episodes on the cutaneous nerve fibers of leprosy patients was assessed in six patients (three with reversal reactions and three with erythema nodosum leprosum). Cryosections of cutaneous biopsy of reactional lesions taken during the episode and of another sample during the remission period were immunostained with anti-NGFr and anti-PGP 9.5 (indirect immunofluorescence). We found no significant statistical difference in the number of NGFr- and PGP 9.5-positive fibers between the reactional and post-reactional groups. A significant difference was detected between the number of NGFr and PGP 9.5-stained fibers inside of the reactional group of biopsy cryosections but this difference was ascribed to the distinct aspects of the nerve fibers displayed whether stained with anti-NGFr or with anti-PGP 9.5; NGFr-positive branches looked larger and so interpreted as containing more fibers. In addition, a substantial number NGFr-positive fibers were PGP 9.5-negative. No differences in the number of stained fibers among the distinct cutaneous regions examined (epidermis + upper dermis, mid and deep dermis) was detected. In conclusion, the number of PGP- and NGFr-positive fibers were not significantly different in the reactional and post-reactional biopsies in the present study. NGFr-staining of the nerve fibers is different from their PGP-imunoreactivity and the evaluation of the nerve fiber status on an innervated target organ should be carried out choosing markers for both components of nerve fibers (Schwann cells and axons).

Mast cell subsets and neuropeptides in leprosy reactions

The immunohistochemical identification of neuropeptides (calcitonin gene-related peptide, vasoactive intestinal polypeptide, substance P, alpha-melanocyte stimulating hormone and gamma-melanocyte stimulating hormone) quantification of mast cells and their subsets (tryptase/chymase-immunoreactive mast cells = TCMC and tryptase-immunoreactive mast cells = TMC) were determined in biopsies of six patients with leprosy reactions (three patients with type I reaction and three with type II). Biopsies were compared with those taken from the same body site in the remission stage of the same patient. We found a relative increase of TMC in the inflammatory infiltrate of the reactional biopsies compared to the post-reactional biopsy. Also, the total number of mast cells and the TMC/TCMC ratio in the inflammatory infiltrate was significantly higher than in the intervening dermis of the biopsies of both periods. No significant difference was found regarding neuroptide expression in the reactional and post-reactional biopsies. The relative increase of TMC in the reactional infiltrates could implicate this mast cell subset in the reported increase of the immune response in leprosy reactions.

Comprehensive evaluation of complement components in the course of type I (Lepra) and type II (ENL) reactions

Complement components C1q and C4 of classic pathway; C3d, a breakdown product of C3, and factor B of alternate pathway: and C3, a component both of classic and alternate pathways, were studied in 35 patients, comprising 18 type I (Lepra) and 17 type II (ENL) reactions. There was a significant decrease in C3 and factor B with a concomitant rise of C3d during ENL. These changes indicate their preeminent role in immunogenesis of type II (ENL) reaction. The changes in the classic pathway components, on the other hand, were insignificant, apparently suggesting its limited involvement in ENL. Furthermore, reversion of factor B and C3d after subsidence of reaction is intriguing and may indicate that they are not substantially affected even with contemporary treatment. Complement components, of both classic and alternate pathways, showed no significant alterations either during type I (Lepra) reaction or after its amelioration.

Immune complex assays: diagnostic and clinical application

The presence of circulating immune complexes have been described in many different human disease states but the significance of their presence has always been a subject for debate. Improvements in the methods of detecting immune complexes have demonstrated a wide degree of heterogeneity, which accounts for the difficulty in obtaining accurate and reproducible measurements, even in the same individual. Techniques for isolating individual complexes, characterizing their pathophysiological properties, and biochemically analyzing the nature of the complexed antigen are now being used to provide data that is helping to clarify the role of immune complexes in the pathogenesis of disease. In addition, such studies are also providing data which is proving that immune complexes have a potential role in immune regulation.