Involvement of TNF-Producing CD8+ Effector Memory T Cells with Immunopathogenesis of Erythema Nodosum Leprosum in Leprosy Patients

Immunogenicity and efficacy of an oral live-attenuated vaccine for bovine Johne's disease

Mycobacterium avium subsp. paratuberculosis (MAP), the etiological agent of Johne's disease (JD) in ruminants, establishes a prolonged and often lifelong enteric infection. The implementation of control measures for bovine JD has faced obstacles due to the considerable expenses involved in disease surveillance and hindered by unreliable and inadequate diagnostic tests, emphasizing the need for an effective vaccine that can stimulate mucosal immunity in the gastrointestinal tract. Previous investigations have demonstrated that deletion of the BacA gene in MAP produces an attenuated strain that can transiently colonize the calf small intestine while retaining its capacity to stimulate systemic immune responses similar to wildtype MAP strains. This study assessed the efficacy of the BacA gene deletion MAP strain, referred to as the BacA vaccine, when administered orally to young calves. The research aimed to evaluate its effectiveness in controlling MAP intestinal infection and to investigate the immune responses elicited by mucosal vaccination. The study represents the first evaluation of an enteric modified live MAP vaccine in the context of an oral MAP challenge in young calves. Oral immunization with BacA reduced MAP colonization specifically in the ileum and ileocecal valve. This partially protective immune response was associated with an increased frequency of CD4+ and CD8+ T cells with a pro-inflammatory phenotype (IFNγ+/TNFα+) in vaccinated animals. Moreover, re-stimulated PBMCs from vaccinated animals showed increased expression of IFNγ, IP-10, IL-2, and IL-17 at 10- and 12-weeks post challenge. Furthermore, immunophenotyping of blood leukocytes revealed that vaccinated calves had increased levels of T cells expressing cell-surface markers consistent with long-term central memory. Overall, our findings provide new insights into the development and immunogenicity of a modified live MAP vaccine against bovine JD, demonstrating oral vaccination can stimulate host immune responses that can be protective against enteric MAP infection.

Downmodulation of Regulatory T Cells Producing TGF-β Participates in Pathogenesis of Leprosy Reactions

Leprosy reactions are an acute and systemic manifestation, which occurs suddenly, can be severe and lead leprosy patients to disability. Reactional episodes are observed among half of the multibacillary patients, mainly in borderline lepromatous and lepromatous forms. They may begin at any time during multidrug therapy, and even before the treatment. Physical disabilities, which are the source of extreme suffering and pain for patients, occur in progression of the cellular immune response associated with a reaction and are still poorly understood. Thus, this work aimed to phenotypically and functionally characterize CD4⁺ and CD8⁺ Treg cells ex vivo and in response to Mycobacterium leprae (ML). We studied 52 individuals, including 18 newly diagnosed and untreated multibacillary leprosy patients, 19 reactional multibacillary patients (Type I or Type II episodes) and 15 healthy volunteers, included as controls, all residents of the city of Rio de Janeiro. The functional activity and frequencies of these cells were evaluated through multiparametric flow cytometry. In addition, the production of cytokines in supernatant from peripheral blood mononuclear cell cultures was also investigated against ML by enzyme-linked immunosorbent assay. Our results showed a decrease in CD4⁺TGF-β⁺ Treg and CD8⁺ TGF-β⁺ Treg in leprosy multibacillary patients during both types of reactional episodes. Alterations in the cytokine profile was also observed in Type II reactions, along with upregulation of IL-17 and IL-6 in supernatant. Thus, our study suggests that downregulation of Treg cells is related with both classes of reactional episodes, improving our understanding of immune hyporesponsiveness in multibacillary patients and hyperesponsiveness in both reactions.

Presence of Senescent and Memory CD8+ Leukocytes as Immunocenescence Markers in Skin Lesions of Elderly Leprosy Patients

Leprosy is an infectious disease that remains endemic in approximately 100 developing countries, where about 200,000 new cases are diagnosed each year. Moreover, multibacillary leprosy, the most contagious form of the disease, has been detected at continuously higher rates among Brazilian elderly people. Due to the so-called immunosenescence, characterized by several alterations in the quality of the immune response during aging, this group is more susceptible to infectious diseases. In view of such data, the purpose of our work was to investigate if age-related alterations in the immune response could influence the pathogenesis of leprosy. As such, we studied 87 individuals, 62 newly diagnosed and untreated leprosy patients distributed according to the age range and to the clinical forms of the disease and 25 healthy volunteers, who were studied as controls. The frequency of senescent and memory CD8⁺ leukocytes was assessed by immunofluorescence of biopsies from cutaneous lesions, while the serum levels of IgG anti-CMV antibodies were analyzed by chemiluminescence and the gene expression of T cell receptors' inhibitors by RT-qPCR. We noted an accumulation of memory CD8⁺ T lymphocytes, as well as reduced CD8⁺CD28⁺ cell expression in skin lesions from elderly patients, when compared to younger people. Alterations in LAG3 and PDCD1 gene expression in cutaneous lesions of young MB patients were also observed, when compared to elderly patients. Such data suggest that the age-related alterations of T lymphocyte subsets can facilitate the onset of leprosy in elderly patients, not to mention other chronic inflammatory diseases.

In search of biomarkers for leprosy by unraveling the host immune response to Mycobacterium leprae

Mycobacterium leprae, the causative agent of leprosy, is still actively transmitted in endemic areas reflected by the fairly stable number of new cases detected each year. Recognizing the signs and symptoms of leprosy is challenging, especially at an early stage. Improved diagnostic tools, based on sensitive and specific biomarkers, that facilitate diagnosis of leprosy are therefore urgently needed. In this review, we address the challenges that leprosy biomarker research is facing by reviewing cell types reported to be involved in host immunity to M leprae. These cell types can be associated with different possible fates of M leprae infection being either protective immunity, or pathogenic immune responses inducing nerve damage. Unraveling these responses will facilitate the search for biomarkers. Implications for further studies to disentangle the complex interplay between host responses that lead to leprosy disease are discussed, providing leads for the identification of new biomarkers to improve leprosy diagnostics.