Fever and Immune Response

Fever is a component of the innate immune system, which is nonspecific in nature.
It affects the entire body and targets all pathogens rather than a specific one.

Bacterial invasion triggers immune response.
- Macrophages identify and destroy bacteria, though this process takes time.
- Bacterial debris and live bacteria release pyrogens.
Pyrogens: Chemicals that stimulate fever.
- They can derive from the bacterial cell wall or be released by macrophages after bacteria destruction.
Cytokines: Pyrogens promote the production of interleukin-1 (IL-1) and interleukin-6 (IL-6), which are crucial in regulating fever.

Hypothalamus regulates body temperature; has a set point usually around 98°F.
When pyrogens are present, IL-1 alters this set point to a higher temperature (e.g., 100°F, 102°F).
Responses to this set point increase include:
- Vasoconstriction: Blood vessels constrict to decrease heat loss, redirecting warmth to the core.
- Shivering: Skeletal muscles contract rapidly to generate heat.
- Behavioral changes: Seeking warmth (e.g., heavier clothing, blankets).

Increased metabolism: After fever onset, the metabolic rate rises, enhancing immune cell function and efficiency.
Inhibitory effect on bacteria growth: Many pathogenic bacteria prefer 98°F for optimal growth; elevated temperatures may slow their replication.
Fever aids in managing infections by increasing immune activity and decreasing bacterial growth rates.

Acetaminophen (Tylenol): Commonly used to reduce fever. Engages COX enzyme to limit cytokine signaling that promotes fever.
- Aspirin also works similarly.
Important to note: Mild fevers can aid in fighting infections; thus, medication should be used judiciously.

Divided into humoral (B cells) and cellular (T cells) components.
B cells produce antibodies which target antigens in blood fluids (extracellularly).
T cells can destroy infected cells directly (intracellularly).

Systemic: Response affects the whole body due to activation of lymphocytes (B and T cells).
Specific: Targeted towards specific pathogens (differentiated B and T cells based on pathogen recognition).
Memory: Remembers past infections for faster and more effective future responses.

Antigens trigger immune response. They can activate both the innate and acquired immune systems.
B cells can detect specific antigens through surface receptors which may include immunoglobulins (IgD, IgM).

Encountering an antigen initiates clonal replication of B cells, producing:
- Plasma cells: Secrete large amounts of antibodies.
- Memory B cells: Persist after the infection, ensuring faster response upon re-exposure.
Antibody production: Plasma cells can produce approximately 2000 antibodies per second.

Primary Response: Slow to develop but generates antibodies and resolves infections.
Secondary Response: Rapid and more robust due to memory cells, leading to higher antibody levels and faster eradication of pathogens.

Vaccinations simulate primary infections; they prepare the immune system to respond quickly to actual pathogens via memory cell activation.
Some treatments involve direct antibody injections for immediate immunity (e.g., antivenom, rabies).

Fever plays a significant role in the immune response, enhancing metabolism, immune efficiency, and inhibiting pathogen growth. Acquired immunity adds a layer of specificity and memory that greatly improves the body's ability to deal with infections over time.