Defence Against Colonization and Infection

Abstract

Man is constantly bombarded with potentially pathogenic viruses, bacteria, fungi and protozoa, yet rarely suffers infection. This is due to the presence of a highly efficient immune system. The classical specific immune system (humoral and cell-mediated) is of prime importance in limiting the duration and spread of infection and, of course, in preventing a second attack by a particular pathogen. Of greater importance in limiting the initial interaction between microbe and man is an amalgam of factors known as the non-specific immune system. These are designed to prevent colonization, to prevent microorganisms gaining access to normally sterile areas, and to limit their spread if such access occurs. Before discussing defences it is necessary to describe the colonization of man by microorganisms.