Immunology: Memory B-Cells

Study Notes

A few activated clone cells develop into moderate numbers of Memory B-cells, similar to the original clone.
These cells do not become plasma cells, but instead circulate throughout the body and populate lymphatic tissue, remaining dormant until re-exposure.
Upon re-exposure to the same antigen, they greatly enhance the population of the clone line for the specific antigen.

Immunoglobulin: a class of protein with a molecular weight of 160,000 to 970,000, present in serum (20% of all plasma proteins), and functions as antibodies.
Each Heavy Chain is paralleled by a Light Chain.
Variable portion of the chain pair is different for each specific antibody and binds to its specific antigen.
Constant Portion determines other properties, such as diffusability, adherence to tissues, or complement.

Antibodies are the antigen-recognition molecules of B cells, made both as:
- Membrane-bound receptors for antigen, the B-cell receptor.
- Secreted (unbound, free) antibodies that bind antigens and elicit humoral effector functions.
Functions of Antibodies:
- Agglutination: Clump antigens together to be more easily destroyed by phagocytes.
- Precipitation: Soluble antigens are precipitated and destroyed by phagocytes.

Activated T-Cells circulate into lymph and blood and throughout the body.
Activated T-Cells continue to circulate for months or years.
Memory T-Cells: Some remain as new T cells similar to the original clone.
Subsequent exposure results in a more rapid and powerful response than the first exposure, due to memory T-Cells spread throughout the body.

MHC is a set of genes that code for cell surface MHC proteins (in humans, aka HLA).
Autorecognition: MHC allows the immune system to bind to, recognize, and tolerate itself.
Determines the compatibility of organ donors.
Main function is to bind to Antigens from pathogens and display them on the cell surface for recognition by T-Cells.
MHC I: present on all nucleated cells, presenting processed Antigens to Cytotoxic T-Cells who express CD8 Receptors.
MHC II: present on Antigen Presenting Cells (Macrophages, Dendritic Cells, and B-cells), presenting processed Antigens to Helper T-Cells who express CD4 Receptors.

Active immunity: the person's own body develops the antibodies or activated T-Cells in response to foreign Antigen.
Passive immunity: transfusion of antibodies or T lymphocytes to confer immunity, lasting only for a few weeks.

Hypersensitivity reactions:
- Exaggerated immune response to a foreign substance, resulting in inflammation or destruction of normal tissue.
- 4 types (I, II, III, IV).
Autoimmune reactions: mistakes self as non-self.

Involved allergens are normally harmless, but re-exposure in certain individuals causes an allergic reaction.
Acquired, predictable, rapid in onset, localized or systemic.
Allergen binds with IgE (bound to) mast cells and basophils, causing anaphylactic degranulation.

Also known as cytotoxic hypersensitivity, killing cells.
Mediated by IgG or IgM and the complement system.
Ab (IgM, IgG) binds to antigen on the patient's own cells, recognized by macrophages and dendritic cells (phagocytes).

Immune complex-mediated, involving IgG, antigen, and complement.
Circulating dissolved antigen binds with IgG antibody, creating Ag/Ab complexes of varying size.
Large complexes are removed by macrophages, while smaller complexes are deposited in tissue, triggering inflammation and tissue destruction.

Delayed hypersensitivity reaction, not antibody-mediated.
Cell-mediated, CD4+ and CD8+, helper T-Cells and cytotoxic T-Cells.
Both T-Cell types recognize antigen:MHC (I&II) complex, activating tissue destruction.

Renin is released by the kidney in response to underperfusion or decreased NaCl delivery.
Renin converts Angiotensinogen to Angiotensin I.
ACE-1 converts Angiotensin I to Angiotensin II.
Angiotensin II causes vasoconstriction and Aldosterone secretion.
Aldosterone saves sodium and water, increasing blood pressure.
ACE-2 converts Angiotensin II to Angiotensin (1-7), which is a vasodilator, anti-inflammatory, and antioxidant.
Blockage of the ACE-2 enzyme receptor by Covid-19 is therefore pro-inflammatory and vasoconstrictive.

Molecular Tests and Antigen Tests: show if you have an active coronavirus infection.
Antibody Tests: look for antibodies made by the immune system in response to a specific virus, but should not be used to diagnose COVID-19 due to the time it takes for antibodies to develop.