Acquired Immunity
Acquired immunity, also called adaptive immunity, is a learned immune response to a specific foreign invader. Once the body becomes exposed to a foreign antigen, acquired immunity kicks in and remembers that information long-term. Many years later, when our immune system sees that same antigen again, it is already prepared for it and can launch a rapid attack. The two main mechanisms for this type of immunity are cell-mediated immunity and humoral immunity, which are both executed by lymphocytes.
Lymphocytes make up about a third of the WBCs in our bodies. Lymphocytes are small cells that can circulate in the blood, but are also able to exist in tissues, essentially roaming freely in the body looking for work. The subtypes of lymphocytes are T-lymphocytes (or T-cells, which play a role in both cell- mediated and humoral immunity) and B-lymphocytes (or B-cells). Some B-lymphocytes become plasma cells, which in response to a particular antigen can remember an invader at a future exposure and produce antibodies to that specific antigen.
Cell-Mediated Immunity (CMI) uses T-lymphocytes as its main weapon, although interaction between T-lymphocytes and B-lymphocytes often occurs. After a foreign invader is digested by a macrophage, it presents details about the antigens on the surface of that microorganism to T- lymphocytes.
One type of T-lymphocyte, the helper T-cell, will bring that information to other T- lymphocytes (so they will recognize the invader), natural killer cells (who will seek out and kill the organism), and B-lymphocytes (who initiates the humoral immune response).
Another type of T-lymphocyte, the cytoxic T-cell, uses a more direct approach and kills cells that it recognizes as non-self or potentially harmful.
Humoral immunity involves the production of antibodies. Antibodies, or immunoglobulins, are proteins produced by B-lymphocyte plasma cells in response to recognition of a specific foreign antigen. Antibodies can prevent viruses from entering healthy cells, neutralize the invader’s toxins, or break down the microorganism and leave them for the scavenger phagocytic cells to get rid of.
Working Together
Immunity is a very complex process that requires interaction between all the mechanisms to be most effective. Phagocytic WBCs, such as macrophages and natural killer cells from our innate immunity, help to make cell-mediated and humoral immunity function properly. However, our innate immune system is only effective in the short-term, and needs our acquired immunity for continued protection.
Sources:
Otto, S. Protective Mechanisms. in Otto, S. ed (2001) Oncology Nursing 4th ed. Mosby:St. Louis. (pp. 917-948).
Williams, L. “Comprehensive Review of Hematopoiesis and Immunology: Implications for Hematopoietic Stem Cell Transplant Recipients” in Ezzone,S. (2004) Hematopoietic Stem Cell Transplantation: A Manual for Nursing Practice. Oncology Nursing Society. Pittsburg, PA (pp.1-13).
