Immune Defence: Microbial Interference

Abstract

The immune system controls the host–microbe interactions, the outcome of which can range from symbiotic coexistence with commensally microbiota, to mild asymptomatic infections, to highly virulent infectious diseases. This control is achieved by two defence mechanisms: the innate immune defence, which consists in a nonspecific mechanism, and the adaptive immunity defence, acquired over time following infections or vaccination. Despite the sophisticated immune system, extracellular and intracellular pathogens have developed numerous, and often ingenious strategies, to evade, interfere or eradicate the effectiveness of host immune defences. Although the strategies used by viral and bacterial pathogens are numerous, there are several general mechanisms shared between these microbial pathogens. The success of each pathogen depends on the coordinated activities of its virulence factors to overcome host barriers to colonisation and its ability to mount an effective anti‐immune response within the infected host, which can ultimately result in acute disease or chronic infection. Key Concepts: Immunoglobulin proteases cleave antibodies rendering them nonfunctional and leading to deficiencies in the immune system. Complement regulators prevent complement activation and cell destruction. Interference with major histocompatibility complexes overcomes T‐cell recognition. Microbial interference with cytokines modulates intracellular signalling critical to the regulation, proliferation and differentiation of lymphocytes, which drive inflammation. Intracellular resistance allows microorganisms to circumvent humoral defence mechanisms and spread within the host. Immunosuppresion reduces T or B lymphocytes’ defence.