Isäntäreaktiot

Isäntäreaktiot, often translated as host reactions, refers to the complex biological responses of an organism (the host) when it encounters a foreign entity, most commonly a pathogen like a virus, bacterium, fungus, or parasite. This reaction is a fundamental aspect of immunology and is crucial for the survival of the host.

The host reaction encompasses a wide range of mechanisms, both innate and adaptive. Innate immunity provides a rapid, non-specific defense. This includes physical barriers like skin and mucous membranes, as well as cellular responses such as phagocytosis by macrophages and neutrophils, and the production of inflammatory mediators. Inflammation, a hallmark of host reaction, involves redness, swelling, heat, and pain, and serves to recruit immune cells to the site of infection.

Adaptive immunity, on the other hand, is slower to develop but is highly specific and provides long-lasting memory. Key components include the production of antibodies by B cells and the cytotoxic activity of T cells. Antibodies can neutralize pathogens directly or mark them for destruction by other immune cells. Cytotoxic T cells can kill infected host cells. The interplay between these innate and adaptive responses determines the effectiveness of the host's defense against the invading agent. The outcome of a host reaction can range from complete elimination of the pathogen to chronic infection or even host death.