Overview of Inflammation and Phagocytosis

The process by which a cell engulfs a particle, such as a bacterium or virus, and destroys it.

An enzyme that breaks down hydrogen peroxide, a toxic by-product of neutrophil activity, into water and oxygen.

A type of white blood cell that plays a crucial role in the immune response.

A mechanism that directly kills infected or abnormal cells without the involvement of antibodies. Examples include cytotoxic T lymphocytes releasing perforins and granzymes.

A type of protein that forms pores in the cell membrane of target cells, leading to their destruction.

White blood cells (WBCs) move from the bloodstream into tissues where pathogens are present, leading to various cellular events such as engulfing and destroying pathogens.

Neutrophils are a type of WBC that engulfs pathogens and destroys them through a process called respiratory burst.

Macrophages are another type of WBC that engulf pathogens, process their contents, and present them on MHC II molecules to other immune cells.

Macrophages that display processed pathogen fragments on MHC II molecules on their surface, allowing them to activate T-helper cells.

A process used by neutrophils, involving the production of reactive oxygen species like H2O2 to destroy pathogens within the phagolysosome.

A defensive mechanism employed by neutrophils, where their DNA is released to trap and kill pathogens, enhancing the ability of other WBCs to phagocytose them.

The widening of blood vessels, often in response to injury or infection. This allows more blood flow to the affected area, aiding in healing.

A localized protective response triggered by tissue injury or infection, characterized by redness, swelling, heat, and pain.

A type of inflammation that is rapid and short-lived. It's the body's initial response to injury or infection, aiming to eliminate the cause and start healing.

A type of inflammation that persists over a long time (weeks, months, even years). It often occurs when the initial cause of inflammation isn't completely resolved.

A type of inflammatory response that occurs when immune cells within the body directly cause damage or inflammation.

A type of inflammatory response triggered by external factors, such as bacteria, viruses, or chemicals.

A type of cell that presents antigens (foreign molecules) to immune cells, triggering an immune response. Macrophages, dendritic cells, and B lymphocytes are examples.

A process where white blood cells (leukocytes) attach to the inner lining of blood vessels in preparation for migrating to the site of inflammation.

Natural killer (NK) cells are a type of lymphocyte that directly kill infected cells without prior sensitization to a specific antigen. They are part of the innate immune system and act as a first line of defense against viral infections.

NK cells can be activated through the major histocompatibility complex (MHC) I complex, which is a protein complex found on the surface of almost all nucleated cells. It displays antigens to immune cells, providing information about the cell's state. Abnormal MHC I expression or absence of MHC I due to viral infection activates NK cells.

When a virus infects a cell, it often alters or inhibits the MHC I complex to avoid detection by the immune system. This abnormal MHC I or lack of MHC I signals NK cells to activate.

Activated NK cells release cytotoxic proteins called perforins and granzymes. Perforins create pores in the cell membrane, allowing granzymes to enter the target cell. Granzymes initiate programmed cell death, or apoptosis, ultimately eliminating the virus-infected cell.

Antibody-dependent cell-mediated cytotoxicity (ADCC) is another way NK cells can be activated. This involves IgG antibodies produced by plasma cells that bind to viral antigens expressed on the MHC I complex of infected cells.

NK cells have a CD-16 receptor that recognizes the Fc portion of IgG antibodies. When NK cells bind to the Fc portion of IgG via CD-16, they are activated and initiate cytotoxic activity.

Activated NK cells in ADCC release perforins and granzymes, which, as mentioned earlier, cause apoptosis of the virus-infected cell.

NK cells are a critical part of the innate immune system, providing rapid defense against viral infections and other threats. Understanding their activation mechanisms is essential for comprehending how our bodies fight off disease.