17.4 Pathogen Recognition and Phagocytosis & 17.5 Inflammation and Fever

What are leukocytes?

Phagocytes that travel to infection sites.

What initiates diapedesis?

Complement factor 5a and cytokines.

What is diapedesis/extravasation?

The process of leukocytes passing through capillary walls to tissues.

What is transendothelial migration?

The flattening out and squeezing through cellular junction after 'rolling adhesion'.

What aids phagocytes in recognizing pathogens?

Complement factors, lectins, and auto recognition for pathogen-associated molecular patterns (PAMPs).

What are some examples of PAMPs?

Peptidoglycan, LPS, flagellin, microbial DNA/RNA, and lipopeptides.

What are pattern recognition receptors (PRRs)?

Structures that allow phagocytic cells to detect PAMPs.

What are Toll-like receptors (TLRs)?

PRRs that bind to PAMPs and communicate with the phagocyte nucleus to elicit a response.

Where are most PRRs located?

On the surface of phagocytes, though some are imbedded internally.

How do PRRs on macrophages respond?

They respond to chemical distress signals from damaged or stressed cells, triggering an inflammatory response.

What happens when a PAMP is recognized by a phagocyte?

The phagocyte activates genes for phagocytosis, cell proliferation, interferon production, and/or cytokines.

What are the stages of phagocytosis?

1. Pathogen engulfment (phagocytosis) 2. Formation of phagosome 3. Formation of phagolysosome and pathogen particle degradation 4. Expulsion of debris.

What is the role of phagocytes in the immune response?

They recognize and engulf pathogens, aiding in the body's defense against infections.

What is the purpose of inflammation?

To recruit immune cells, eliminate dead/damaged cells, and initiate repair of host damage.

What characterizes acute inflammation?

Immediate response to a breach in physical barrier, causing erythema, edema, heat, pain, and altered function.

What happens during chronic inflammation?

Occurs when acute inflammation is insufficient; infection sites may be walled off with white blood cells (granulomas).

What is a systemic inflammatory response?

A response that raises overall body temperature, often referred to as fever.

What are pyrogens?

Substances produced by pathogens that alter the hypothalamus, regulating body temperature.

What are the two types of pyrogens?

Exogenous (from outside the body, e.g., LPS) and endogenous (produced by the body, e.g., interleukins from leukocytes).

What physiological responses occur during fever?

Vasoconstriction and shivering occur initially, followed by vasodilation and sweating during the crisis phase.

What can happen if the immune response is too strong?

It can cause tissue and organ damage, such as in cases involving superantigens.

What is the role of fever in the immune response?

Enhances innate immune defenses and inhibits the growth of mesophile pathogens.

What is the crisis phase of fever?

The phase when fever breaks, leading to vasodilation and sweating.

Fever

A temporary increase in body temperature, often due to an illness or infection.

Exogenous pyrogen

Substances originating outside the body that induce fever, such as lipopolysaccharides (LPS) from bacteria.

Endogenous pyrogen

Fever-inducing substances produced within the body, such as interleukins released by leukocytes.

Lipopolysaccharides (LPS)

Molecules found in the outer membrane of Gram-negative bacteria that can trigger an immune response, Exogenous pyrogen

Interleukins from leukocytes

A group of cytokines produced by leukocytes that play a crucial role in the immune response and can act as endogenous pyrogens.