Macrophages in host defence--an overview

The importance of macrophages in host defence is well documented. They are distributed in various tissues where they perform functions in normal steady state as well as in diseased condition. Macrophages secrete a number of enzymes, plasma proteins, complement and coagulation factors which regulate the effector functions of the macrophages. Exposure of macrophages to pathogens results in further metabolic changes which activate the former to secrete oxygen metabolites leading to their augmented microbicidal activity. Macrophages respond to the external stimuli by expressing a large repertoire of surface receptors which play an important role in the activation, recognition and endocytosis of foreign microorganisms. A large number of intracellular pathogens are harboured in the macrophages which can reside and replicate in them. A variety of strategem has been employed to target drugs to vacuolar apparatus of the macrophages in order to combat intracellular pathogens. This review covers some of these aspects particularly in relation to hose defence and methods by which therapeutic agents could be specifically delivered to macrophages.