Strategic targets of essential host-pathogen interactions.

This review summarizes the present concepts regarding the biological processes that mediate intrinsic and innate host defense against microbial invasion of the lung. Innate immunity is the first line of defense of the higher organisms towards invading pathogens. It accomplishes a wide variety of activities including recognition and effector functions. The innate responses use phagocytic cells (macrophages, monocytes, and neutrophils), cells that release inflammatory mediators (basophils, mast cells, and eosinophils), and natural killer cells. The molecular component of innate responses includes complement, acute-phase proteins, and cytokines. Recognition of pathogen-associated molecular patterns is mediated by the pathogen receptors of the innate immune system, among these molecules toll-like receptors have emerged as fundamental components in the innate immune responses to infection, and a link between innate and adaptive immunity. Additional protection comes from polypeptide mediators of the innate host defense, such as the defensins and other antibiotic peptides. In view of the considerable burden in terms of mortality and morbidity that severe infections still pose worldwide, a better understanding of the biological basis of host-pathogen interactions opens stimulating future treatment perspectives.