Study of the receiver LILRA2 in the maturation and production of cytokines for dendrític cells and its envolvement in leprosy.
LILR (Leukocyte Immunoglobulin- like Receptor) are a family of receptors from the immunoglobulin superfamily expressed on myeloid and lymphoid cells. LILR are characterized by either 2 or 4 homologous Immunoglobulin-like domais. One subset of receptors, LILRB, displays long citoplasmatic tails containing immunoreceptor tyrosine-based inhibitory motifs (ITIM). These receptors inhibit cell activation by recruiting protein tyrosine phosphatase SHP-1. Another subset of receptors, LILRA, contains short cytoplasmatic domain that lack recognizable docking motifs for signalling mediators. These receptors associate with the gamma chain of the Fc receptor, which transduces stimulatory signals by recruiting protein tyrosine kinases through a cytoplasmatic immunoreceptor tyrosine-based activation motif (ITAM). A third subset of receptors has no transmembrane domain and is secreted as a soluble receptor. Some of these receptors, LILRB1 and LILRB2, are specific receptors for MHC class I molecules. LILRBs have been shown to inhibit cell activation in several experimental systems. Little is know about the activating receptors. LILRA2 was found to be up-regulated in lesions of lepromatous leprosy patients. In order to clarify whether this receptor might influence the immune response in leprosy, the function of this receptor was investigated. Cross-linking of LILRA2 on dendritic cell (DC) caused an up-regulation on protein tyrosine phosphorylation, suggesting LILRA2 stimulates intracellular signaling. Upon cross-linking, DC express high levels of MHC I and II and co-stimulatory molecules, but cytokines were not detected on culture supernatant. However, a strong synergistic effect on TNF and IL-10 production was observed when cells were simultaneously stimulated by LILRA2 and TLR4 or CD40. LILRA2 activated DC also induced allogeneic T lymphocytes proliferation. By double immunofluorescence labeling, it was identified that LILRA2 is expressed on macrophage-like CD68+cells in lepromatous leprosy skin lesions. The capacity of M. leprae to induce DC activation and/or to modulate LILRA2-induced activation was further investigated. In functional experiments it was observed that M. tuberculosis but not M. leprae stimulated cells induce TNF secretion. IL-10 was detected on M. leprae-stimulated cultures, albeit at lower level than that of M. tuberculosis-stimulated cells. M. leprae had no synergistic effect on LILRA2 activated cells. To identify LILRA2 ligand, a tetramer was generated and it?s binding to different cell types was tested. The tetramer interacted with IL-4 stimulated monocytes and DC. Although Immunoprecipitation experiments were preformed, the ligand was not successfully identified. The data obtained so far indicates that LILRA2 activation enhances DC maturation markers expression and cytokine secretion by activated DC. M. leprae is not a potent DC activator. The high surface levels of co-stimulatory molecules, the presence of IL-10 and absence of IL-12 suggest that DC stimulated by M. leprae or LILRA2 are only partially activated and they might contribute to lepromatous leprosy tolerance.
Advisor:Elizabeth Pereira Sampaio
School:Faculdades Oswaldo Cruz
Source Type:Master's Thesis
Tumor Necrosis Factor
Date of Publication:08/27/2007