Innate Immunity Responses

Vocabulary:
- Granuloma: A walled-off pocket of infection that contains dead cells and pathogens, often surrounded by white blood cells.
- Pyrogen: Substances that induce fever by causing an increase in the body temperature.
- Immune Specificity: The ability of the immune system to target specific pathogens.
- Immune Memory: The capacity of the immune system to remember past infections and respond more effectively upon re-exposure.
- Antigen: Any particle, molecule, or cellular component that can trigger an adaptive immune response.
- Epitope: A small, three-dimensional shape that is characteristic for antigens and is the specific part recognized by antibodies.
- Hapten: A small molecule that, when combined with a larger carrier such as a protein, can elicit an immune response.
- Adjuvant: A substance that enhances the body's immune response to an antigen.
- Antibody Variable Region: The part of the antibody where antigen binding occurs, allowing for the specificity of the antibody to various antigens.
Outline how innate immunity can fail in fighting infections and describe how granulomas transition from an immune problem to a broader health issue.
Briefly describe the pathway from immune stimulus to bodily fever.
Identify the two primary characteristics of the adaptive immune system.
Characterize the relationship between antigens and epitopes.
Reading Material: OpenStax Chapter 17.4 and 18.1.

Innate Immunity
- Physical, Mechanical, and Microbiome Barrier Functions.
- Non-specific Cells (Granulocytes and Agranulocytes).
- Signals and Inflammation (Chemical Signals and Fever).
Bridge to Adaptive Immunity.

Acute Inflammation:
- Sometimes fails to clear pathogens or particles from the target site, leading to chronic inflammation.
- Chronic inflammation can manifest as granulomas, which are essentially pockets of infection.
- Granulomas consist of dead cells and pathogens, and they are particularly significant in tuberculosis infections.
- The same mechanism of chronic inflammation is seen in cirrhosis, where scar tissue forms in the liver over time.

Co-opting Mechanisms:
- Certain pathogens exploit phagocytosis for their survival, such as Leishmania tropica, which causes cutaneous leishmaniasis.
- Massive granulomas develop in the skin to contain this parasite in susceptible individuals.
- Listeria monocytogenes can escape from phagocytes (through listerolysin O) due to its ability to break out from amoebae in its natural environment.
- HIV uses macrophages for entry into the body by utilizing phagocytosis.
Questioning Phagocytosis Failure: What happens if phagocytosis does not clear the infection?

Chemical Signals:
- These signals can travel beyond the local environment, often initiating a cascade of responses.
- The immune system amplifies its response, leading to the attraction of varied leukocytes and lymphocytes to the site of infection and nearby lymph nodes.
- This chemotactic process may also contribute to homeostatic mechanisms necessary for hematopoiesis.
- This amplification is a crucial aspect of bridging innate responses to adaptive immunity.

Exogenous Pyrogens:
- Substances like LPS provoke strong chemical responses from leukocytes, leading to the generation and diffusion of endogenous pyrogens.
- This cascade promotes the production of prostaglandins, which are targeted by NSAIDs to reduce fever.
- If endogenous pyrogens reach the hypothalamus, fever is induced.

**Impact on Pathogens: **
- Elevated body temperatures inhibit bacteria by pushing them away from optimal growth temperatures, causing slower growth.
- Heat increases vulnerability of pathogens to stress, including iron deprivation and exposure to complement proteins.
Enhanced Immune Cell Function:
- Neutrophils and macrophages move more rapidly in elevated temperatures.
- Phagocytic activity increases, leading to more effective pathogen clearance.
- Enzymes in granulocytes and lymphocytes function more effectively during fever.
- The intensity of tissue antiviral responses increases, and dying damaged cells deprive invading pathogens of resources.

Lymphatic Vessels:
- Form a one-way system that conducts lymph from tissues back to the circulatory system.
Composition of Lymph:
- It consists of a liquid similar to blood plasma and arises from fluid leaked from blood vessels into surrounding tissues.

Overview:
- A major flaw in innate immunity is its static response, which does not adapt when pathogens evolve to evade defenses.
- The adaptive immune response provides specificity for unique pathogens and adapts to new challenges (
- It recognizes unique molecular structures characterized by microbes.
- The hallmark of adaptive immunity is memory, allowing for a heightened response upon subsequent exposures to the same pathogens.
- B cells and T cells serve as the primary effectors in adaptive immunity.

Definition of Antigens:
- Any particle, molecule, or cellular component capable of triggering an adaptive immune response.
Definition of Epitopes:
- Small three-dimensional shapes that are characteristic of antigens and are the specific sites recognized by antibodies.

Primary vs Secondary Responses:
- The secondary immune response is characterized by enhanced amplification of immune function, marking the strength of the adaptive immune response upon re-exposure to the same pathogen.