In: Anatomy and Physiology
Explain what is happening at the cellular level (including the cell types involved) in the following events of active adaptive immunity:
a. Antigen presentation: During this process, antigen-presenting cells including dendritic cells or macrophages detect substances released when beta-cells, bacterial cells or viral molecules go through the process of cell death. As a prompt response, large amounts of inflammatory molecules and T-cell stimulators are produced.
b. Antigen detection: The antigen-detection molecules of B cells are called immunoglobulins, or which are abbreviated as Ig. These proteins are produced by B cells in a range which spans several of antigen specificities. Each B cell produces an immunoglobulin of a single specificity when an antigen is detected.
c. Activation of helper T cells: After antibody detection, the helper T cells do not directly kill infected cells, as opposed to the action of cytotoxic T. Instead, T helper cells activate the cytotoxic T cells and macrophages, hich in turn attack the infected cells. Alternatively, the T cells stimulate B cells to secrete antibodies.
d. Production of antibodies by B cells: Antibodies are produced in response to antigens, by a special group of white blood cells called B cells. When an antigen binds to the surface of the B-cell, it acts as a stimulus for the B cell to divide and transform into a group of identical cells which are known as clones. These mature B cells are now known as plasma cells and these plasma cells secrete antibodies into the lymphatic system.
Identify and describe how antigens are eliminated following the formation of an antigen-antibody complex using the following mechanisms:
a. Activation of complement system: Once activated, a series of proteins come into play, in order to generate an enzyme C3 convertase, which cleaves the C3 protein. After a series of other other steps in the cascade, the C5 protein is cleaved.
b. Attraction of phagocytes: As a result of the above step, these cleaved products accumulate and this signals phagocytes to reach the target cells, which have been tagged for elimination by the process of phagocytosis or cell eating.
c. Opsonization: Opsonization is the process in which a particle which is to be eliminated by the process of phagocytosis, is coated with proteins. This coating serves as a signal to tissue macrophages and activated follicular dendritic cells, which in turn perform phagocytosis.
d. Stimulating inflammation: Some of the causative factors that stimulate inflammation are microbes, environmental agents, chemicals, and sometimes, tissue death. The most common cause of inflammation are infectious agents such as viruses and microorganisms. Bacteria release special substances called endotoxins that bring about inflammation. Other environmental factors such as trauma, burns or even radioactive exposure can damage tissues.
e. Preventing bacterial or viral adhesion: High quality coatings which are prepared from polymers including several siloxanes or acetates are capable of inhibiting the bacterial colonization on surfaces