Figure 1.

Hypothetical model of a T_H2 dominated adoptive immune response and local T_H2 promoting micromilieu induced by pollen-associated lipid mediators. When pollen grains are hydrated on the respiratory epithelia, they release allergens and eicosanoid lipids, the so-called pollen-associated lipid mediators (PALMs). Leucotrien-like PALMs have the potential to attract and activate innate cells like neutrophils and eosinophils, while prostaglandin-like PALMs, the phytoprostanes, and possibly other pollen-derived factors, can modulate the migratory and T helper cell polarizing capacities of resident dendritic cells. In addition, DCs exposed to PALMs might be induced to secrete chemokines which preferentially recruit further T_H2 cells to the site of pollen exposure. Taken together, the possible effects of PALMs on both cells of the innate and the adoptive immune system might lead to a local microenvironment favoring T_H2 responses. I FN-γ = interferon-γ; IL = interleukin; PC = plasma cell