Introduction The immune system is considered the first line of defense in the human body against various pathogens, including bacteria. The role of bacteria is not limited to causing diseases; some types play an important role in supporting and regulating the immune system. Recent studies have shown a close relationship between bacteria and immune function. Definition and Types of Bacteria Bacteria are microscopic living organisms found in various environments, including the human body. They are classified into: • Beneficial bacteria: Naturally live in the intestines and on the skin and help support the immune system. • Harmful bacteria: Cause diseases when they enter the body or multiply abnormally. The Immune System and Its Functions The immune system consists of a complex network of cells and tissues and functions to: • Recognize foreign bodies • Fight infections • Produce antibodies • Develop immune memory to combat future infections Role of Beneficial Bacteria in Supporting Immunity Beneficial bacteria, especially gut bacteria, play a fundamental role in: • Stimulating immune cells • Enhancing antibody production • Preventing the growth of harmful bacteria • Regulating inflammatory responses They also contribute to strengthening the intestinal barrier, which prevents harmful microorganisms from entering the bloodstream. Effect of Harmful Bacteria on the Immune System When harmful bacteria enter the body, the immune system activates a defensive response that includes: • Inflammation • Cytokine secretion • Activation of phagocytic cells If the immune system is weakened, bacterial infections may lead to serious complications. Bacterial Balance and Its Immunological Importance An imbalance between beneficial and harmful bacteria, resulting from poor nutrition or excessive use of antibiotics, leads to weakened immunity and increased susceptibility to diseases and recurrent infections. Role of Nutrition and Lifestyle A healthy lifestyle supports beneficial bacteria and the immune system through: • Consuming fiber-rich foods • Drinking adequate amounts of water • Reducing processed food intake • Practicing physical activity • Avoiding the random use of antibiotics Conclusion It is evident that bacteria have a dual role in affecting the immune system, as they can either support health or cause disease. Maintaining bacterial balance is one of the key factors in enhancing immune efficiency and preventing diseases, highlighting the importance of health and nutritional awareness in an individual’s life. Al-Mustaqbal University The First University in Iraq