Host factors affecting disease transmission.

In prevention of transmission of infectious disease, the host uses a variety of protective mechanisms and can elicit many different responses. Nonspecific defense mechanisms include an intact integument (skin and mucous membranes). The host also can use specialized substances it may secrete, such as mucin or fatty acids to prevent colonization or to inhibit growth of potential pathogens. Specialized surface structures are also used by the host in prevention of disease transmission. These structures include cells composed of keratin and cells with cilia. Additionally, nonspecific protection can be achieved through the actions of the host's nonpathogenic microflora. If these nonspecific barriers to microorganism invasion are breached, other host interactions occur. Complement has many nonspecific actions that may be used to control invasion of microorganisms. PMLs are an additional line of defense the host has available in prevention of infection. These cells are responsible for intracellular killing of pathogens through the use of enzymatic and oxidative mechanisms. The mononuclear phagocyte system allows for elimination of foreign material and debris from the inflammatory reaction. Additionally, the macrophages process and present antigens to T lymphocytes. B lymphocytes differentiate to produce plasma cells, which produce specific antibodies aimed at the invading microorganism. T lymphocytes are involved in the killing of pathogenic microorganisms and in the production of powerful immune modulators known as lymphokines. Fever and inflammation also serve to stimulate reactions aimed at destroying and removing the pathogen from the host system. These factors all play an important role in prevention of disease transmission in a human host.