Cross-talks within the innate immune system: the role of neutrophils

Neutrophils represent a key component of the inflammatory response and act as a powerful defensive system against invading bacteria. Following activation by various stimuli, neutrophils have the capacity to release lytic enzymes with potent antimicrobial potential and to generate reactive oxygen intermediates, both essential for pathogen killing. Neutrophils can also produce, upon appropriate stimulation, a variety of proteins in vitro and in vivo, including cytokines and chemokines, that are involved in their effector functions, as well as in the recruitment, activation and programming of other immune cells. In this latter context, recent studies have shown that neutrophils, through secreted products and/or cell-cell contact, might potentially interact with monocytes, dendritic cells and NK cells, T and B lymphocytes, in turn suggesting that neutrophils play an important role in the development and/or modulation of the immune response. In the context of the innate immune system, for instance, it has been demonstrated that neutrophils, under specific settings: i) induce dendritic cell maturation and activation; ii) release chemokines strongly chemotactic for immature dendritic cells; iii) deliver antigen molecules to dendritic cells, thus eliciting antigen-specific T lymphocytes responses. On the other hand, the interaction of neutrophils with either NK cells or T cell subsets is less documented and somewhat contradictory. Nonetheless, the concept that cooperation between cells of the innate immune system is important in sculpting the ensuing inflammatory response and that neutrophils actively participate in this process is continuously better supported. It is thus our purpose to provide additional experimental evidence which extends the current knowledge of neutrophils as cells involved in the cross-talks with other leukocyte types