Immunology and Serology Fundamentals

Comprehensive flashcards covering antigens, the development of the immune system, immunoglobulin classes, vaccine types, hypersensitivity reactions, transplant immunology, and serological testing methods.

Antigen (Ag)

Any molecule capable of stimulating an immune response that is recognized as foreign (non-self) and triggers the activation of B cells and/or T cells.

Epitope

Also known as the antigenic determinant, this is the small part of an antigen actually recognized by immune cells.

Alloantigens

Antigens that vary among members of the same species; they are critical in blood transfusions and organ transplantation.

Superantigens

Antigens that cause an extremely strong T-cell response, leading to massive cytokine release, toxic shock, and organ failure.

Autoantigens

Normal body molecules that are mistakenly attacked by the immune system, occurring in autoimmune diseases.

Tolerance

The immune system's ability to distinguish between self and non-self molecules.

PAMPs

Found only on microbes and recognized by innate immunity to trigger second line defenses.

Thymus

The primary lymphoid organ where T cells undergo maturation.

MALT, GALT, and SALT

Secondary lymphoid organs: Mucosa-associated, Gut-associated, and Skin-associated lymphoid tissues where immune responses usually begin.

Dendritic Cells

Professional antigen-presenting cells (APCs) that phagocytize pathogens and act as the major link between innate and adaptive immunity.

MHC (Major Histocompatibility Complex)

A protein found on cell surfaces that displays antigen to T cells; T cells remain "blind" to antigens without it.

HLA (Human Leukocyte Antigen)

The human version of MHC used for tissue matching and organ transplantation.

Cell-Mediated Immunity

A branch of adaptive immunity driven by T cells that targets intracellular bacteria, virus-infected cells, and cancer cells directly.

Humoral Immunity

A branch of adaptive immunity driven by B cells that produces antibodies to target extracellular bacteria and toxins.

Helper T Cells (TH)

Considered the "coach" of the immune system; they release cytokines to activate B cells, macrophages, and cytotoxic T cells.

Cytotoxic T Cells (TC)

Immune cells that kill infected cells by releasing perforins to punch holes in the target cell membrane.

Natural Killer Cells

Innate immune cells that lack antigen specificity but kill cancer cells and virus-infected cells.

Plasma Cells

The "antibody factories" derived from B cells that produce and secrete immunoglobulins.

Fab Region

The "fragment antigen binding" region of an antibody responsible for binding to a specific antigen.

Fc Region

The part of the antibody that attaches to immune cells like macrophages or mast cells and can activate complement.

IgG

The most abundant antibody ($80\%$) that crosses the placenta and dominates the secondary immune response.

IgA

An antibody found in secretions like tears, saliva, and breast milk that protects mucosal surfaces.

IgM

A large pentamer and the first antibody produced during the primary immune response.

IgD

An antibody that acts as a B-cell receptor and is involved in the development and activation of B cells.

IgE

The antibody responsible for allergic reactions and defense against parasitic worms by binding to mast cells and basophils.

Primary Antibody Response

The slow immune response occurring upon the first exposure to an antigen, characterized by a low titer and initial production of IgM.

Secondary (Anamnestic) Response

A rapid, stronger immune response upon re-exposure to an antigen, characterized by high titers of IgG due to memory cells.

Active Immunity

Long-lasting immunity where the individual's own immune system produces antibodies and memory cells.

Passive Immunity

Temporary protection provided by receiving pre-made antibodies from another source, such as through the placenta or antivenom.

Live Attenuated Vaccines

Vaccines containing living organisms with reduced virulence, providing strong, long-lasting immunity; examples include MMR and Sabin Polio.

Toxoid Vaccines

Vaccines made from inactivated exotoxins to protect against the toxin rather than the bacteria itself, such as Tetanus and Diphtheria.

Herd Immunity

A state where a sufficient portion of the population is immune to prevent the spread of a disease.

Hypersensitivity

An exaggerated or inappropriate immune response to an allergen that results in tissue damage.

Type I Hypersensitivity

Immediate allergy mediated by IgE, mast cells, and histamine; examples include anaphylaxis and asthma.

Type II Hypersensitivity

Antibody-mediated cytotoxic reaction involving IgG, IgM, and complement, such as blood transfusion reactions.

Type III Hypersensitivity

Immune complex-mediated reactions where IgG/IgM complexes become trapped in tissues, causing inflammation; examples include Lupus and Serum Sickness.

Type IV Hypersensitivity

Delayed hypersensitivity mediated by T cells rather than antibodies, typically appearing $24-72\,\text{hours}$ after exposure, such as the TB test.

RhoGAM

An Rh immune globulin given as passive immunity to Rh- mothers to prevent Hemolytic Disease of the Newborn (HDN).

Autograft

A tissue transplant where the donor is also the recipient, resulting in no rejection.

Allograft

The most common transplant type, performed between two different humans who are not identical twins.

Graft-versus-Host Disease (GVHD)

A condition occurring mainly in bone marrow transplants where the donor T cells attack the recipient's tissues.

Agammaglobulinemia

A primary immunodeficiency characterized by a lack of B cells and antibodies, leading to recurrent bacterial infections.

DiGeorge Syndrome

A primary immunodeficiency where the thymus fails to develop, resulting in a lack of mature T cells.

SCID (Severe Combined Immunodeficiency)

A genetic condition where both B cells and T cells are non-functional, often fatal without a marrow or stem cell transplant.

Oncogenes

Mutated or abnormally activated normal genes that regulate cell growth and can cause cancer.

Immune Surveillance

The process where the immune system constantly searches for and destroys abnormal or transformed cells.

Serology

The study of antibodies and antigens in serum to diagnose infections and determine immune status.

Indirect ELISA

A serological test used specifically to detect the presence of patient antibodies in a sample.

Sandwich (Capture) ELISA

A serological test used to detect the presence of a specific antigen (the germ itself).