The document summarizes the immune response process. When a germ gets past physical barriers, the immune system responds by (1) macrophages engulfing infected cells, (2) macrophages signaling T cells and B cells, (3) B cells producing antibodies that destroy viruses outside cells and signal other cells to destroy viruses as well. The body develops immunity by remembering how to make antibodies for each disease encountered, so if a disease is encountered again the body can quickly fight it off. This is why people rarely get diseases like chickenpox twice.