Adaptive Immunity and Hypersensitivity Lecture Notes

Practice questions covering the characteristics of adaptive immunity, types of hypersensitivity reactions (I-IV), and the pathophysiology of HIV/AIDS.

What constitutes the third line of defense in the body?

Adaptive immunity, often called the immune response, which consists of lymphocytes and serum proteins called antibodies.

How does the adaptive immune response compare to the innate inflammatory response in terms of speed and specificity?

The adaptive immune response develops more slowly than inflammation but is exquisitely specific to a particular infectious agent.

Which cells are responsible for humoral immunity?

$B$ cells (or $B$ lymphocytes), which act through circulating antibodies.

What is the role of $T$ cells in cell-mediated immunity?

They kill targets directly or stimulate the activity of other leukocytes.

What term refers to the extensive diversity of antigen receptors on $B$ and $T$ cells that allows them to recognize different antigens?

Clonal diversity.

Into which three functional subsets do $T$ cells develop?

$T$-cytotoxic ($T_c$ cell), $T$-helper ($Th$ cell), and $T$-regulatory ($Treg$ cell).

What is the difference between active and passive immunity?

Active immunity is produced by an individual after natural exposure or immunization, while passive immunity involves transferring preformed antibodies or $T$ lymphocytes from a donor to a recipient.

What immunologic changes are associated with aging?

Deficient $T$-cell activity, inferior antibody production to specific antigens, and increased levels of circulating autoantibodies.

How is alloimmunity defined?

Immune responses directed against beneficial foreign tissues, such as transfusions or transplants.

What is the most rapid immediate hypersensitivity reaction?

Anaphylaxis, which occurs within minutes of reexposure to an antigen.

In Type I hypersensitivity, what occurs when antigens cross-link $IgE$ on the surface of mast cells?

Mast cell degranulation and the release of histamine and other inflammatory substances.

What are the effects of histamine acting through the $H1$ receptor?

Bronchial constriction (contracting bronchial smooth muscles) and increased vascular permeability (causing edema and vasodilation).

List the five mechanisms of Type II (tissue-specific) hypersensitivity reactions.

1. complement-mediated lysis, 2. opsonization and phagocytosis, 3. neutrophil-mediated tissue damage, 4. antibody-dependent cell-mediated cytotoxicity, 5. modulation of cellular function.

What causes the tissue damage observed in Type III hypersensitivity reactions?

The formation of immune complexes that deposit in target tissues, activate the complement cascade, and attract neutrophils that release lysosomal enzymes.

What characterizes Type IV (cell-mediated) hypersensitivity?

A delayed reaction mediated by lymphocytes and macrophages rather than antibodies; examples include contact sensitivity to poison ivy or metals.

Which surface receptor on HIV binds to the $CD4$ molecule on $T$-helper cells?

The envelope glycoprotein $gp120$.

What is the function of the enzyme reverse transcriptase ($RT$) in the HIV life cycle?

It converts the viral RNA into a double-stranded DNA.

What enzyme is responsible for inserting new viral DNA into an infected cell's genetic material?

Integrase.

What is the major immunologic finding in patients with AIDS?

A striking decrease in the number of $CD4^+$ $Th$ cells.

What does the acronym HAART stand for in the context of HIV treatment?

Highly active antiretroviral therapy.