Host responses refer to the ways in which an organism's immune system reacts to and defends against pathogens or other foreign substances. This field of research focuses on understanding the complex interactions between the host organism and the invading microbe or foreign substance, and how the host's immune system detects and responds to these threats. Researchers studying host responses often investigate the mechanisms by which the immune system recognizes and targets pathogens, the production of specific immune cells and molecules in response to infection, and the overall immune response that leads to either successful clearance of the pathogen or the development of disease. By studying host responses, researchers can gain insights into how the immune system functions in health and disease, and develop new strategies for diagnosing and treating infections, autoimmune disorders, and other immune-related conditions.