Host immune responses are the body's defense mechanisms against pathogens, such as bacteria and viruses. When a pathogen enters the body, the immune system recognizes it as foreign and activates various cells, including T cells and B cells. These cells work together to identify, attack, and eliminate the invaders, helping to prevent infections. The immune response can be divided into two main types: innate immunity and adaptive immunity. Innate immunity provides immediate, non-specific defense, while adaptive immunity develops over time and targets specific pathogens. This dual approach ensures that the body can respond effectively to a wide range of threats.