Immunology Concepts Quiz

Immunity is protection from something, making you unaffected or unbothered.
Immunity is the body's ability to defend itself from external or internal threats.
The immune system is a set of cells (mostly WBCs) and tissues (spleen, lymph nodes) that resist infection and harmful effects from other living things.
Immune mechanisms identify pathogens and neutralize their threat.

The immune system can recognize many disease-causing agents, like viruses, bacteria, and parasites.
The immune system can differentiate between the body's healthy cells and foreign cells.
Blood cells play a crucial role in immunological surveillance. These cells include T lymphocytes (Helper-T, Killer-T, and Natural Killer (NK)), B lymphocytes, thrombocytes, erythrocytes, neutrophils, basophils, eosinophils, macrophages, and monocytes.
Various tissues are part of the immune system, such as the thymus, tonsils, adenoids, bone marrow, spleen, lymph nodes, and the gastrointestinal tract (Peyer's patches, appendix).

Immunity can be classified into innate and adaptive immunity.
Innate (natural) immunity is non-specific, has a first line of defense (skin, mucous membranes, normal flora), and a second line (innate immune cells, inflammation, complement, antimicrobial substances).
Adaptive (acquired) immunity is specific, has a third line of defense (specialized lymphocytes: B cells, helper T cells, killer T cells).

Innate immunity includes cells (leukocytes) and mechanisms (inflammation, phagocytosis) naturally present in healthy people to defend against infection.
Natural barriers of infection, such as skin, enzymes in mucus/tears/saliva, coughing/sneezing, cilia in the respiratory tract, and the acidic environment of the stomach, also contribute to defense.
Inflammation is a crucial response to infection or irritation; it's stimulated by chemical factors released by injured cells, establishes a physical barrier to infection, and promotes healing.
Inflammation is initiated by resident macrophages, dendritic cells, histiocytes, and mast cells when an infection, burn, or injury occurs. They release inflammatory mediators (e.g., histamine, bradykinin, serotonin, prostaglandins). These mediators sensitize pain receptors, cause vasodilation, and attract phagocytes (especially neutrophils), causing symptoms like pain, swelling, redness, hotness, and altered function.
Phagocytes are immune cells that engulf (phagocytose) pathogens or particles. They patrol the body and react to cytokines/chemokines from other cells.
Phagocytic cells—macrophages, neutrophils, and dendritic cells—are crucial components of innate immunity. Phagocytosis involves a phagocyte extending its membrane to surround and engulf a particle/pathogen, forming a phagosome that fuses with a lysosome containing enzymes to kill and digest the particle/pathogen.

Adaptive immunity is a specific response to a particular pathogen.
It creates immunological memory after an initial response, leading to an enhanced response to re-infection.
It’s acquired during life (in utero or post-birth).
It is classified into passive and active acquired immunity.
Passive immunity involves receiving antibodies from another source (e.g., mother to infant). Active immunity results from the immune system’s own response to an infecting or harmful agent. Both can be acquired naturally or artificially (through vaccines).

Lymphocytes (B cells and T cells) are produced in bone marrow but mature in different locations (B cells mature in bone marrow, T cells mature in the thymus gland).
B cells are responsible for antibody production (humoral immunity).
T cells are responsible for cell-mediated immunity (cellular immunity).
- Different types of T cells exist; examples include helper T cells (Th), cytotoxic T cells (CTL), and T-regulatory cells (T-regulator)

MHC is a set of cell surface proteins essential for the immune system to recognize foreign molecules.
MHC molecules bind to antigens from pathogens and display them on the cell surface for recognition by T cells.
The MHC determines donor compatibility for organ transplants and susceptibility to autoimmune diseases.
MHC family is divided into Class I (MHC-I) and Class II (MHC-II) subgroups.
Class I MHC molecules are recognized by CD8 co-receptors, while Class II MHC molecules are recognized by CD4 co-receptors.

Antigens were initially defined as foreign molecules inducing antibodies.
Immunogen is a more comprehensive term, referring to any substance capable of stimulating an immune response, which encompasses not only antibody production but other immune reactions.
A true antigen is typically a foreign protein of good molecular size.
Haptens are small molecules that aren't antigenic by themselves but become antigenic when combined with larger molecules.
The immune reaction targets both the hapten and the carrier protein.

Antibodies are proteins produced in response to a specific antigen and react only with that antigen.
Antibodies are Y-shaped glycoproteins produced by activated B cells, aiding in identifying and neutralizing pathogens.
They can be secreted or remain on the B cell surface.
Typically consist of two large heavy chains (H chains), and two small light chains (L chains) linked by disulfide bonds.
- Each chain has a constant (C) and variable (V) region; V regions/sites bind to antigens.
Different classes/types of Immunoglobulins (Ig) exist, including IgA, IgD, IgE, IgG and IgM. Different classes have specific roles in immunity.

Immune reactions occur between immunogens (antigens) and their specific antibodies, either in vivo or in vitro.
Reactions are specific, meaning each antibody reacts with only one specific antigen.
Reactions often need optimum temperature (37°C) and equivalent concentrations of antigen and antibody to be seen effectively.
Different types of immune reactions exist, including agglutination, precipitation, and others, dependent on the nature of the antigen. A range of tests rely on these reactions. Agglutination reactions occur when particles are clumped by antibodies. Precipitation occurs with soluble antigens.