Immune System and the Body’s Defense

A comprehensive set of flashcards covering infectious agents, innate and adaptive immunity, lymphocyte activation, and immunologic memory based on Chapter 22 lecture notes.

What are the five major categories of infectious agents?

Bacteria, viruses, fungi, protozoans, and multicellular parasites.

What are the three common shapes of bacteria?

Spherical (cocci), rodlike (bacilli), and coiled (spirilla).

What is the typical size range of a bacterial cell?

$1 \text{ to } 2\thinspace\text{µm}$.

Why are viruses described as obligate intracellular parasites?

Because a virus must enter a cell to reproduce, directing the host cell to copy its nucleic acid and capsid.

What are prions and what is an example of a disease they cause?

Prions are fragments of infectious proteins that cause disease in nervous tissue; an example is Variant Creutzfeldt-Jakob disease (‘mad cow’).

Where are leukocytes formed in the body?

Red bone marrow.

What are the three modes of cytokine action?

Autocrine (acts on the same cell), paracrine (acts on local cells), and endocrine (acts on distant cells via the blood).

How do innate and adaptive immunity differ in their response time?

Innate immunity responds immediately, while adaptive immunity takes several days to be effective.

Which cells are the primary phagocytes in the innate immune system?

Neutrophils, macrophages, and dendritic cells.

How do Natural Killer (NK) cells eliminate unwanted cells?

By releasing cytotoxic chemicals: perforin to create a pore and granzymes to induce apoptosis.

What is the role of interferons (IFNs) in the immune response?

They are cytokines that nonspecifically impede viral spread by stimulating neighboring cells to synthesize enzymes that destroy viral nucleic acids.

What are the two pathways of complement activation?

Classical pathway (antibody binds to antigen) and Alternative pathway (complement binds to bacterial or fungal cell wall polysaccharides).

What is opsonization?

The binding of a complement protein (opsonin) to a pathogen to enhance the likelihood of phagocytosis.

What are the five cardinal signs of inflammation?

Redness, heat, swelling, pain, and loss of function.

What defines a fever (pyrexia) in terms of temperature?

An elevation of $1^℃$ or more from the normal body temperature of $37^℃$.

What are the three stages of a fever?

Onset, stadium, and defervescence.

What are the specific risks associated with high fevers at $106^℉$ and $109^℉$?

Irreversible brain damage occurs at temperatures greater than $106^℉$, and death is likely if the temperature exceeds $109^℉$.

What is the difference between cell-mediated and humoral immunity?

Cell-mediated immunity involves T-lymphocytes, while humoral immunity involves B-lymphocytes, plasma cells, and antibodies.

What is a hapten?

A small foreign molecule that induces an immune response only when attached to a carrier molecule in the host.

Which T-lymphocyte subtype is identified by the CD4 protein?

Helper T-lymphocytes.

Where are MHC class I and MHC class II molecules found?

MHC I is found on all nucleated cells; MHC II is found on professional antigen-presenting cells (APCs).

What percentage of T-cells are typically eliminated during thymic selection?

98\text{%}.

What is the difference between positive and negative selection during T-lymphocyte maturation?

Positive selection tests for the ability to bind MHC molecules; negative selection tests for the ability to NOT bind self-antigens (self-tolerance).

How many antigen-binding sites are typically found on most antibodies?

Two.

What are the five major classes of immunoglobulins?

IgG, IgM, IgA, IgD, and IgE.

Which immunoglobulin class is the most prevalent in the blood?

IgG, which makes up 75\text{–}85\text{%} of blood antibodies.

What is the primary function of IgA?

It is found in mucus, saliva, tears, and breastmilk to prevent pathogens from adhering to and penetrating epithelial linings.

What is the difference between active and passive immunity?

Active immunity results from direct exposure to an antigen and forms memory cells; passive immunity is obtained from another individual and does not produce memory cells.

What is an example of artificial passive immunity?

The transfer of serum containing antibodies against snake venom.

What happens to the helper T-lymphocyte count in individuals with AIDS?

The helper T-lymphocyte count drops below a certain level, making the individual susceptible to opportunistic infections.