👉 Infection occurs when a pathogen, such as a virus or bacterium, enters a host's body and begins to multiply, often causing harm or disease. This process typically involves the pathogen attaching to host cells, either by binding to specific receptors on the cell surface, and then either injecting its genetic material or directly taking over the cell's machinery to replicate itself. The host's immune system may respond by attempting to eliminate the invader, but if the infection is successful, it can lead to symptoms and potential complications. For example, a common cold virus infects respiratory epithelial cells, causing inflammation and mucus production, while HIV targets and destroys CD4+ T cells, weakening the immune response over time. Understanding these transactions is crucial for developing treatments and preventive measures against infectious diseases.
