Endocrine and metabolic manifestations associated with infectious and inflammatory diseases.

Abstract

There are three important factors in the emergence or re-emergence of infectious diseases: microbial factors, host factors and factors related to the transmission of microbes. This paper will review host natural and adaptive defense mechanisms and discuss experimental evidence regarding the effectors of endocrine and metabolic responses to infection. External defense mechanisms protect against the first step in infection, entry of the pathogen into the host. The skin is a very powerful barrier to most infectious agents, and although mucosal linings of the respiratory, gastrointestinal and urogenital tracts are more delicate, they have the advantage of specialized defense mechanisms, such as the secretion of factors like immunoglobulins and mucus, and the sweeping action of cilia. Together these external defenses are of the utmost importance to hosts vulnerable to infection. If a pathogen succeeds in entering the body, the next step in host defense is natural immunity (Table 1). Natural immunity is less sophisticated than adaptive immunity, but it is a very important defense against all types of infection in many animal species. The principal cellular components of natural immunity are phagocytes, such as macrophages, neutrophils, natural killer cells and mast cells; the principal soluble factors are components of the complement cascade, interferon and acute-phase reactants. Humoral factors are of differing importance in different types of infection, due, in part, to the fact that microbes have evolved a variety of different mechanisms to escape the host's natural defenses. View this table: Table 1 Host defense mechanisms against infectious agents The third line of defense in higher vertebrates is adaptive immunity which is specific to the invading organism. It is a tailor-made defense system. Three types of cells — antigen-presenting cells, such as macrophages, T cells and B cells — are involved in adaptive immunity. The relative importance of cellular immunity, mediated by T cells, or humoral …