The impairment in Antigen Presenting Cells differentiation induced by Mycobacterium tuberculosis is characterized by low DC-SIGN and MR expression involving TLR-2 activation and IL-10 secretion at a monocytic level.

BALBOA L; ROMERO M; YOKOBORI N; SCHIERLOH P; GEFFNER L; BASILE J; ROLDÁN N; MUSELLA R; ABBATE E; DE LA BARRERA S; SASIAIN MC; ALEMÁN M

Berlín

Congreso; Second European Congress of Immunology; 2009

The differentiation of dendritic cells (DC) from monocytes (Mo) has been studied recently suggesting a target of escape for pathogens. We investigated possible mechanisms triggered by Mycobacterium tuberculosis (Mtb) responsible for the impairment in DC and macrophages (MΦ) differentiation. For this purpose human Mo were cultured with IL-4 and GM-CSF in presence of irradiated-Mtb (MtbDC), IL-10 (IL10DC), aIL-10 plus Mtb (aIL10MtbDC) or Pam3 (Pam3DC) for 6 days. Also, Mo were cultured with GM-CSF in presence (MtbMΦ) or not of Mtb (MΦ). Thereafter, phenotype was evaluated by flow cytometry. Proliferation assays were performed by culturing Mtb-maturated APC with allogeneic (MLR) or autologous (specific response, from PPD+ individuals) lymphocytes for 5 days. Our results showed that MtbDC and MtbMΦ were characterized by high CD14/CD86 and low CD1a/CD1b expression and displayed a high MLR (P< 0.05) and a low specific proliferation (P< 0.05). Furthermore, the lower CD1b levels the weaker specific proliferation detected (P< 0.05). Mtb induced a DC population which lost DC-SIGN and MR receptors (the two main receptors that mediate Mtb up-take), and a Mϕ population with reduced MR expression (P< 0.05). CD1a/CD14 profile was affected when Mtb was added throughout the first day of DC differentiation and not by latter addition (P< 0.05). We wondered if IL-10 production and TLR-2 activation (Pam3 ligation) were involved in DC differentiation impairment. Mtb induced doses-dependent production of IL-10 in MtbDC (P< 0.05). Moreover, IL10DC showed high levels of CD14 which was counteracted in aIL10MtbDC (P< 0.05). Finally, Pam3DC led to a CD1a/CD1b reduction and a CD14 increase showing a lower specific proliferation (P< 0.01) as MtbDC did. TLR2 ligation triggers p38 activation, and we found that p38 inhibition in MtbDC partially restored the phenotype by increasing CD1a and diminishing CD14 levels (P< 0.05). We conclude that Mtb subverts human Mo differentiation at early differentiation stages. This strategy triggered by Mtb involves partially IL-10 secretion and TLR-2 activation. Thus, Mo may constitute an Mtb target to evade the immune system by developing APC deficient in DC-SIGN and MR as well as in CD1 molecules driving poor mycobacterial-specific T-cell response in tuberculosis.