Question

List 5 molecules and cell types that are shared and interconnect the Innate defenses of the body with the Acquired/Adaptive Immunity pathways. Define the defensive functions of each shared component and explain how they connect the immune and innate pathways.

Answer 1

Innate and adaptive immune responses are components of an integrated system of host defense in which numerous cells and molecules function cooperatively. The mechanisms of innate immunity provide effective initial defense against infections. However, many pathogenic microbes have evolved to resist innate immunity, and their elimination requires the more powerful mechanisms of adaptive immunity. There are numerous connections between the innate and adaptive immune systems. The innate immune response to microbes stimulates adaptive immune responses and influences the nature of the adaptive responses. Conversely, adaptive immune responses often work by enhancing the protective mechanisms of innate immunity, making them more capable of effectively combating pathogenic microbes.

The innate leukocytes include: natural killer cells, mast cells, eosinophils, basophils; and the phagocytic cells include macrophages, neutrophils, and dendritic cells.  The cells of the adaptive immune system are lymphocytes – B cells and T cells. B cells, which are derived from the bone marrow, become the cells that produce antibodies.

Natural Killer cells (NK cells), do not attack pathogens directly. Instead, natural killer cells destroy infected host cells in order to stop the spread of an infection. Infected or compromised host cells can signal natural kill cells for destruction through the expression of specific receptors and antigen presentation.Mast cells are found in mucous membranes and connective tissues, and are important for wound healing and defense against pathogens via the inflammatory response. When mast cells are activated, they release cytokines and granules

The phagocyte is also known as an antigen-presenting cell because after engulfing the invading microbe, it displays pieces of protein from the microbe, called antigens, on its surface, on what is known as the major histocompatibility complex (MHC) molecule. This alerts the adaptive immune system and allows cells known as T cells to recognize an infected cell. Inorder to trigger the full adaptive immune response, There also needs to be a danger signal or flag displayed on the surface of the cell to call the adaptive immune system into action. This is the job of proteins called pattern-recognition receptors (PRRs). Found on or inside phagocytes, PRRs recognize general groups of microbes that have common traits. They set in motion a sequence of cellular events that results in posting the flags required to trigger an adaptive immune response. They also release a family of chemical messengers called cytokines to call the adaptive immune system into action.

Adaptive immune responses are carried out by white blood cells called lymphocytes. There are two broad classes of such responses , antibody responses and cell-mediated immune responses, and they are carried out by different classes of lymphocytes, called B cells and T cells, respectively.  In antibody responses, B cells are activated to secrete antibodies, which are proteins called immunoglobulins. The antibodies circulate in the bloodstream and permeate the other body fluids, where they bind specifically to the foreign antigen that stimulated their production . Binding of antibody inactivates viruses and microbial toxins by blocking their ability to bind to receptors on host cells. Antibody binding also marks invading pathogens for destruction, mainly by making it easier for phagocytic cells of the innate immune system to ingest them. In cell-mediated immune responses, the activated T cells react directly against a foreign antigen that is presented to them on the surface of a host cell. The T cell, might kill a virus-infected host cell that has viral antigens on its surface, thereby eliminating the infected cell before the virus has had a chance to replicate . In other cases, the T cell produces signal molecules that activate macrophages to destroy the invading microbes that they have phagocytosed.