Host defense mechanisms are biological processes that protect an organism from harmful pathogens, such as bacteria, viruses, and parasites. These mechanisms include physical barriers like skin and mucous membranes, as well as immune responses that involve white blood cells and antibodies. Together, they work to identify and eliminate foreign invaders, ensuring the body's health and stability. In addition to these innate defenses, organisms also develop adaptive immunity over time. This involves the creation of specific antibodies and memory cells that recognize previously encountered pathogens. Vaccination is a common method to enhance this adaptive response, preparing the immune system for future infections.