Immune system consists of group of cells which acts as soldiers of our body and protects from all types of allergies. As we know, our immune system is the defense mechanism of our body. It protects body from various invaders – bacteria, pathogens, germs, allergies and what not. The immune system is a system that works internally first by recognizing cells or other agents as either 'self' or 'non–self'; this is the first job of the immune system.
Once it recognizes a cell/agent as non–self it will go on to either destroy it or neutralize it. These agents that are non–self are generally foreign agents that have entered the body or abnormal cells somewhere in the body that it is not supposed to be or have mutated.
Phagocytosis is an important feature of cellular innate immunity performed by cells called 'phagocytes' that engulf, or eat, pathogens or particles. Phagocytic cells ingest microbes that penetrate external innate defenses and help trigger an inflammatory response. Complement proteins, interferons and other antimicrobial proteins also act against invading microbes. In local inflammation, histamine and other chemicals released from injured cells promote changes in blood vessels that allow fluid, more phagocytes and anti–microbial proteins to enter the tissues. Natural killer (NK) cells can induce the death of virus–infected or cancer cells via apoptosis (programmed cell death). The innate leukocytes include the phagocytes (macrophages, neutrophils and dendritic cells), mast cells, eosinophils, basophils and natural killer cells. These cells identify and eliminate pathogens, either by attacking larger pathogens through contact or by engulfing and then killing microorganisms.