Increased antigen presentation and T(h)1 polarization in genetically histamine-free mice

Histamine is a well-known inflammatory mediator exerting various immunomodulatory effects and affecting the development of antigen-specific immune responses. Dendritic cells (DCs) are the most potent antigen-presenting cells specialized for capture, uptake, transport, processing and presentation of antigens to T cells. Using a genetically histamine-free [histidine decarboxylase knockout (HDC-/-)] mouse model, we examined the effects of histamine on DC-mediated antigen presentation. Applying an in vitro antigen presentation assay, we found that spleen DCs, derived from HDC-/- mice, display a higher efficiency in antigen presentation compared with wild-type cells. Flow cytometric characterization of DCs disclosed that this difference was not due to an altered distribution of DCs between or within the major functional sub-populations (assessed by CD11b and CD4 as myeloid and CD8 alpha and DEC205 as lymphoid DC markers) or major changes in the co-stimulatory molecule profile (CD40, CD80, CD86). However, real-time PCR analysis of in vivo CFA-induced IL-12p35, IFN gamma, IL-10 and IL-4 expression showed that DCs matured in a histamine-free environment exhibit significantly elevated levels of IL-12p35 and IFN gamma mRNA. In vitro investigations confirmed that isolated DCs, developed in the absence of histamine, exhibit indeed a predominantly T(h)1-polarized cytokine pattern, as they show elevated levels of IFN gamma mRNA upon LPS stimulation. Similar difference was found at the protein level by ELISA, as well. Our study demonstrates that histamine interferes with antigen presentation and alters the cytokine profile of DCs.