Here is a brief overview of how the human immune system works:

• The immune system is made up of cells, tissues, and organs that work together to defend the body against infection.

• The main components are white blood cells (lymphocytes and phagocytes), the spleen, thymus gland, lymph nodes, bone marrow, and lymphatic system.

• There are two main branches - innate immunity and adaptive immunity. Innate immunity provides immediate defense but no memory. Adaptive immunity has specificity and memory.

• Innate immunity involves physical and chemical barriers like skin, mucus, stomach acid, etc. It includes phagocytes that engulf pathogens.

• Adaptive immunity involves B cells that produce antibodies, and T cells that directly attack infected cells. Antibodies target specific pathogens for destruction.

• Antigen presenting cells display foreign pathogen pieces to T cells to trigger an immune response. Memory T and B cells remain after infection to provide faster response if the pathogen is encountered again.

• The immune response is regulated by cytokines and other signaling molecules to balance protection with avoiding autoimmunity.