Immune reactions are the body's responses to harmful substances, such as bacteria, viruses, or toxins. When these invaders enter the body, the immune system identifies them as threats and activates various cells, including white blood cells, to fight off the infection. This process can involve inflammation, where blood flow increases to the affected area, helping to deliver immune cells to where they are needed. There are two main types of immune reactions: innate immunity and adaptive immunity. Innate immunity is the body's first line of defense, providing immediate but non-specific responses. In contrast, adaptive immunity develops over time and involves a targeted response, including the production of antibodies that specifically recognize and neutralize pathogens.