Answer to Question #134047 in Biology for emily byington

Question #134047

Describe the actions of our immune response. what is an antigen? what does it do?

Expert's answer

1. Describe the actions of our immune response.

a) Skin

It acts as a mechanical barrier and prevents the entry of microbes into the body. Intact skin prevents the penetration by most pathogens. The presence of normal microbial flora of the skin prevents colonization or attachment of harmful pathogens.

b) Mucous membrane

 It lines the respiratory, digestive, gastrointestinal tracts, genitourinary tract, and the eyes. Several non-specific mechanisms at the mucosal surface level prevent the entry of microbes. E.g., saliva and tears contain antibacterial and antiviral substances. Mucous secretions are viscous. It traps organisms so that the microbes are prevented from contacting the mucous membrane and penetrate the host.

c) PH

 Many microorganisms cannot live at very low PH. The stomach's acidic environment is harmful to many microorganisms that enter along with food and water through the mouth.

d) Inflammatory mechanisms

The entry of microbes into the body following injury leads to inflammatory responses. Vasodilation allows more blood to flow to the injured site. The cells lining the vessel retract, resulting in gaps between the cells. Phagocytes and fluid from blood leak out and accumulate around the infected area. They play an essential role in the elimination of microbe and subsequent tissue repair.

e) Phagocytic mechanisms

Phagocytosis is the ingestion or engulfment of particulate matter by cells. Phagocytic cells include monocytes, macrophages, and Neutrophils. Phagocytosis has four main mechanisms: Chemotaxis, opsonization and adherence, engulfment/ingestion, and destruction, either oxygen-dependent or oxygen-independent.

f) Enzymes and soluble proteins of innate immunity

 They are produced in large quantities at the time of need. They act on some targets on the surfaces of microbes. They generally recognize the carbohydrate or lipid molecules on the surface of microbes. They include; Lysozymes, acute phase proteins, C reactive proteins, complement, and mannose-binding protein.

g) Humoral Immunity

 It is mediated by antibodies that are produced by B lymphocytes. It protects against circulating extracellular antigens such as bacteria and microbial exotoxins in their extracellular phase. Sensitized B cells proliferate and mature into plasma cells and memory B cells. The plasma cells secrete various antibodies such as IgA, IgG, IgM, IgD & IgE. The memory B cells persist in circulation and are involved in memory function, in secondary immune response, and are resistant to re-infection.

(h)Cell-mediated immunity

T lymphocytes and their secretory products mediate it. It protects against intracellular parasites such as viruses. It is also essential in the rejection of organ transplants and tumor cells. The trigger is the presence of an antigen which is taken up by antigen-presenting cells(APCs) to a resting T cell which becomes sensitized T cell and differentiates into different subpopulations T-helper 1(Th1), T-helper 2 (Th2), T-cytotoxic (Tc) cells, T regulatory (Treg) cells, or T delayed hypersensitive (TDH) cells. Th2 cells produce cytokines that activate B cells to produce antibodies. Th1 produces inflammatory cytokines, while Tc cells are involved in the direct killing. TDH is involved in delayed hypersensitivity, and Treg is involved in the regulation of immune responses.

2. What is an antigen? What does it do?

Antigens – Self or non-self agents capable of stimulating an immune response and reacting with the products. Their presence in the body triggers an immune response.

The antigen-presenting cells (APCs) cleave the foreign protein antigens into small peptides and then present to the T cells. 

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