Lymph notes

Natural killer (NK) cells identify and destroy abnormal or infected cells.
- They secrete proteins called perforins that create holes in target cells.
- Following perforin activity, granzyme enzymes enter through the holes to digest the cell from the inside:
  - Break down DNA and proteins.

The action of granzymes triggers apoptosis, or programmed cell death, in the target cell.
Once the cell is destroyed, the NK cell can move on to target other cells.
After abnormal cells are eliminated, macrophages clean up the debris left by the dead cells.

Abnormal or mutated cells can proliferate quickly if not controlled by NK cells, potentially leading to cancer.
The lymphatic system plays a crucial role in the spread of cancer cells, as these cells can enter lymphatic vessels.
Natural killer cells are distributed throughout all connective tissues in the body, not limited to lymph nodes or spleen.

Interferons are key cytokines released from virally infected cells that signal to nearby cells.
- They alter other cells to prepare them for potential infection and can trigger apoptosis in infected cells.
Interferons enhance the immune system's ability to respond to infections, particularly viruses.

In addition to NK cells, macrophages and other immune cells are activated by interferons to seek out and eliminate infected cells.
Uninfected cells that receive interferon will destroy their RNA, effectively mitigating the virus's ability to replicate.

The complement system helps in immune response through three activation pathways:
- Classical pathway: Uses specific antibodies for activation.
- Alternative pathway: Activated by proteins like C3, which is always present in tissues and blood.
- Lectin pathway: Lectin binds to carbohydrates on bacterial surfaces for activation.

The splitting of C3 produces two fragments:
- C3a: Promotes inflammation by activating basophils and mast cells, releasing histamine.
- C3b: Involved in opsonization, enhancing phagocytosis by macrophages and neutrophils.

C3b also leads to the formation of the membrane attack complex, which creates pores in pathogens, causing cell lysis.
Immunity clearance involves removing antigen-antibody complexes using red blood cells, which transport them to the liver and spleen for destruction.

Fever is a vital response to infection, activated by both exogenous and endogenous pyrogens.
- Exogenous: Chemicals from pathogens trigger the initial fever response.
- Endogenous: Produced inside the body by immune cells, sustaining high temperature until the infection resolves.
Increased body temperature enhances immune function and inhibits pathogen replication.

The inflammatory response includes:
- Chemokines released from injured cells signal for neutrophil migration to the injury site (chemotaxis).
- Neutrophils arrive first, releasing reactive oxygen species to eliminate pathogens.
- Macrophages later clean up the damage and initiate tissue repair through growth factor release.
Typical signs of inflammation include redness, warmth, swelling, pain, and limited movement.

B cells: Produce antibodies that tag pathogens for destruction but do not kill by themselves.
T cells: Can directly kill infected or cancerous cells via cytotoxic mechanisms (e.g., perforins and granzymes).
Helper T cells: Activate other immune cells by releasing signaling molecules.
Regulatory T cells: Inhibit immune responses once the infection is under control, preventing excessive damage.

Immunological memory allows for a rapid response upon re-encountering pathogens.
Vaccinations facilitate the development of memory cells against pathogens:
- Active Immunity: Immunity developed after natural infection or vaccination, leading to memory (long-lasting).
- Passive Immunity: Temporary immunity acquired from another source (e.g., maternal antibodies).
- Important to note: Vaccines aim to protect against diseases that could be life-threatening rather than preventing infection completely.
- Annual flu shots are necessary due to the virus's frequent mutations, requiring updated vaccines to match circulating strains.