Epidermal Langerhans cells (LCs), “sentinels” of the epithelium, undergo increased mobilization from oral mucosa in lichen planus, hairy-leukoplakia and gingivitis/periodontitis, presumably towards lymph nodes. The ability of LC to induce immunoregulatory(toleragenic)/immunostimulatory effector responses may depend on the epithelial cell (EC) microenvironment in which they are “educated”

Objective: To determine the influence of EC and cytokines on LC activation/phenotype in response to microbial challenge.

Hypothesis: LC conditioned with IL-10-secreting EC will optimally blunt LC activation in response to E.coli LPS

Methods: Human primary isolated neonatal-foreskin-EC (keratinocytes) transduced with bi-cistronic-retroviral-vectors-vIL10-IRES-GFP (81% transduction efficiency) or non-transduced EC were conditioned by co-culture (3days) with FACsorted CD1a^+ve CD34-HPC-derived human LC, then pulsed with E.coli LPS (18 hrs). Controls included no LPS, each cell-type alone and LC+hIL-10 and LC/EC+hIL-10. Non-adherent LCs and trypsin-recovered adherent EC/tEC were imaged, FACS-analyzed and supernatants analyzed for cytokines.

Results:(1) tEC secrete 55.37 ng vIL-10/hr/10⁶cells (2) LCs express CD86 constitutively, and are activated by E.coli LPS (↑CD86) (3) EC alone do not activate LCs, but↓ constitutive CD86, and do not prevent LPS-mediated ↑CD86; (4) tEC induces ↓CD86 on LC by 2-fold; moreover, LPS-induced CD86 was abrogated by tEC; (5) tEC vIL-10 is as effective as hIL-10+EC in ↓CD86. Unexpected and provocative results suggest that tEC (but not EC or hIL-10) induce LC to de-differentiate towards a more tolerogenic phenotype (↓CD1a). However, EC+hIL-10+LPS induce ↓CD1a on LC, suggesting both EC and IL-10 are involved in optimal LC conditioning, which makes physiologic sense, as LCs are epithelium-resident cells.

Conclusion: These results suggest that the epithelial cell microenvironment and the presence of IL-10 may play roles in conditioning Langerhans cells towards a tolerogenic phenotype by blunting constitutive/inducible expression of antigen-presenting molecules. A similar strategy is used by Melanoma cells that secrete IL-10 and ↓CD1a on dendritic cells (Gerlini et al. 2004).

NIH/NIDCR-R01-DE14328(CWC), NIH-DEO4511(LBT)