Successive Intramuscular Boosting with IFN-Alpha Protects Mycobacterium bovis BCG-Vaccinated Mice against M. lepraemurium Infection

Abstract

Leprosy caused by Mycobacterium leprae primarily affects the skin and peripheral nerves. As a human infectious disease, it is still a significant health and economic burden on developing countries. Although multidrug therapy is reducing the number of active cases to approximately 0.5 million, the number of cases per year is not declining. Therefore, alternative host-directed strategies should be addressed to improve treatment efficacy and outcome. In this work, using murine leprosy as a model, a very similar granulomatous skin lesion to human leprosy, we have found that successive IFN-alpha boosting protects BCG-vaccinated mice against M. lepraemurium infection. No difference in the seric isotype and all IgG subclasses measured, neither in the TH1 nor in the TH2 type cytokine production, was seen. However, an enhanced iNOS/NO production in BCG-vaccinated/i.m. IFN-alpha boosted mice was observed. The data provided in this study suggest a promising use for IFN-alpha boosting as a new prophylactic alternative to be explored in human leprosy by targeting host innate cell response.

Figure 1

Schematic representation of the prime-boost protocol designed for the study. Adult BALB/c mice were s.c. primed with PBS or 5 × 10⁵ CFUs BCG. Four weeks later, in consecutive days (30, 31, and 32 days), the mice of each group received PBS or 100 UI IFN-α i.m. Mice were rested for 10 weeks and then challenged by intradermal route with 2 × 10⁶ M. lepraemurium. Eight weeks after challenge, mice were sacrificed and skin lesion development was measured.

Figure 2

Histopathological appearance of the lesions (representative results) in the skin of BCG-primed/IFN-alpha boosted and infected mice with M. lepraemurium ((a) right panel), or BCG-vaccinated/PBS-boosted and infected mice with M. lepraemurium ((a) left panel). Sections were stained with Ziehl-Neelsen and Harris'-Hematoxylin (blue) (×40) (a). Graphics of the skin lesion size in MLML infected mice (b). A difference of ^∗ P < 0.05 was considered statistically significant.

Figure 3

Representative results of the inflammatory area in the granuloma and oxide nitric production in serum of the infected mice with M. lepraemurium. Eight weeks after intradermal MLM infection, mice were sacrificed and skin lesions were obtained. Inducible Nitric Oxide Synthase (iNOS, red), NT (green), Gr-1 (White) expression were measured by immunofluorescence (a). Graphics of the inflammatory area (a) and nitric oxide concentration in serum of uninfected, MLM-infected, BCG-vaccinate, IFM-alpha-boosted and BCG-vaccinated/IFN-alpha boosted mice (b) are shown. A difference of ^{∗, ∗∗} P < 0.05 was considered significant.