b'This immune process of ingesting antigens by dendritic cells, macrophages, and neutrophils provides innate immunity. After killing the microbe, phagocytic cells return to the lymph nodes to start their next course of action: stimulating other cells of the immune system to activate acquired immunity.Acquired immunity begins after a phagocytic cell eats an antigen. The phagocyte then signals the next group of immune cells, T and B lymphocytes, to spring into action. Our acquired immune response is critical because it dictates how we respond to foreign substances. Lymphocytes:Lymphocytes, or white blood cells, are mainly composed of T and B lymphocytes. T-cells act on virus-infected body cells and also attack fungi and parasites. In addition, T-cells are an important part of the immune systems destruction of cancerous cells. After being triggered by a phagocyte, T-cells attach to the antigenic cell and inject a protein that kills it. This efficient and powerful action is the central feature of cell-mediated immunity against foreign invaders. Helper T-cells:Helper T-cells are enablers. When stimulated into action by a phagocyte, helper T cells stimulate T- or B-cells to destroy the antigen. Helper T-cells are known as TH1 cells. Those that stimulate B-cells are known as TH2 cells. When activated, specifically primed B-cells multiply rapidly and mature to become plasma cells. Plasma cells are factories for an outpouring of antibodies directed against a specific antigen. This type of immune reaction, involving B-cells, is referred to as humoral immunity. In fact, B-cell antibodies are the basis for immunization. A vaccine contains weakened or fake antigens that trigger the formation of primed B-cells. When the body is later exposed to the real antigen, the primed B-cell is ready to make millions of antibodies directed against the offender. Antibodies:Antibodies are proteins that are released from plasma cells into the blood. Once triggered, these proteins discharge molecules called cytokines. Cytokines act as messenger molecules and also trigger an antigen-killing attack by cytotoxic T-cells and natural killer cells. Natural killer cells destroy antigens by releasing cytotoxins (cell-killing poisons) directly into these unhealthy cells. When Things Go Wrong Immune impairment can be life-threatening. The four basic types of immune disorders are:Immunodeficiency disordersresult when a part of the immune response is impaired. Many immunodeficiency disorders are acquired during life as the result of infections (like HIV) or certain immunosuppressive drugs such as those that are recommended for people who have had organ transplants. Autoimmune disorders,multiple sclerosis, lupus, rheumatoid arthritis, celiac disease, or Hashimotos thyroiditis, result from impaired regulatory T-cells and/or an over-active immune response. Autoimmune diseases range in severity and typically cause on-going, and often worsening, symptoms over many years.Allergiesoccur when the immune system overreacts to an environmental allergen, like dust mites, pollen, or animal dander. Upon repeated exposure, the immune reactivity can cause inflammation of the airways. Other manifestations of allergies are sinusitis, eczema, or anaphylaxis.Cancers of the immune systemoccur when an immune cells DNA is damaged, and then the cell multiplies in an uncontrolled manner. Cancers of the immune system include lymphoma, leukemia, and myeloma.IMMUNITY3'