Immunology #2: Innate Immunity

This statement is true because regardless of the pathway (classical, lectin, or alternative) that activates the complement system, they all converge at the same point, which is the cleavage of C3 into C3b and C3a. This cleavage is an essential step in the complement cascade, leading to the opsonization of pathogens, recruitment of immune cells, and inflammation. Therefore, regardless of the initiating pathway, the end result is the same.

TLR-3 is located within the cell and is responsible for recognizing the double-stranded RNA of viruses. On the other hand, TLR-4 is located on the outside of the cell and is responsible for recognizing LPS (lipopolysaccharide) on gram-negative bacteria.

An opsonin is a substance that enhances the process of phagocytosis by marking pathogens or other foreign particles for destruction by immune cells. Antibodies, produced by the immune system in response to an infection or vaccination, can act as opsonins by binding to pathogens and facilitating their recognition and engulfment by phagocytes. Therefore, an antibody is indeed an example of an opsonin.

The alternative C3 convertase enzyme is also known as C3bBb.

Type 1 interferon alpha and beta are known to have antiviral effects. They are released in response to viral infections and play a crucial role in inhibiting viral replication. They increase resistance to viral replication by inducing the expression of various antiviral proteins within infected cells. Additionally, they enhance the activity of natural killer (NK) cells, which are important in killing virus-infected cells. Therefore, the action of decreasing resistance to viral replication is not associated with Type 1 interferon alpha and beta.

Anaphylatoxins are small proteins that are generated during the activation of the complement system. They play a crucial role in inflammation and immune response. C3a and C5a are both examples of anaphylatoxins. They are produced when the complement protein C3 and C5 are cleaved, respectively. These anaphylatoxins can induce the release of histamine from mast cells, leading to vasodilation, increased vascular permeability, and recruitment of immune cells to the site of inflammation. Therefore, C3a and C5a are correct answers for examples of anaphylatoxins. C3b and C5b, on the other hand, are not anaphylatoxins but rather components of the complement system involved in opsonization and formation of the membrane attack complex, respectively.

In a health person, C3 is always in high concentrations in the body. However, mannose-binding lectin and C-reactive protein increase levels during inflammation explaining their later role in the response to infection.

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