Innate and Active Immune Responses

Innate Immunity

Born with it; do not have to develop it.

Pathogen

Causative agent; anything causing disease.

Leukocytes

White blood cells (WBC) that are essential in the immune response.

Macrophages

Large phagocytic cells that ingest and digest pathogens. (type of WBC)

Neutrophils

The foot soldiers of the immune system; they are white blood cells that perform phagocytosis. 50-70 % of the WBC

Phagocytosis

The process of engulfing and digesting pathogens.

Cytokines

Chemicals released by white blood cells that facilitate communication in immune responses.

Chemokines

A type of cytokine that attracts other white blood cells to an infected area.

First Line of Defense

Includes skin and mucous membranes that act as barriers to pathogens.

Inflammation

Increased blood flow and capillary permeability in response to tissue damage or infection.

Complement System

A group of ~30 proteins that assist with pathogen elimination via opsonization and activation of inflammatory responses.

Adaptive Immunity

Develops after birth and is specific to particular pathogens.

Antigen

Foreign substance that generates an immune response.

APC (Antigen Presenting Cells)

White blood cells that present antigens to activate other immune cells.

Helper T Cells

Lymphocytes that alert other immune cells to activate them.

Killer T Cells

Immune cells that kill infected body cells. (Also Known as Cytotoxic T Cells)

B Cells

Cells that manufacture antibodies.

Antibodies

Y-shaped protein produced by B cells, part of the immune response. Highly Specific, as they can only bind to one antigen. They can Initiate the Complement System, perform Viral inhibition, Neutralize Toxins, Increase Phagocytosis, and Clump up the Pathogens.

Memory Cells

Long-lived cells that remember past infections and can mount a rapid response on re-exposure. They react to the antigen without having to be activated by other immune cells.

Secondary Antibody Response

Rapid and efficient antibody production upon re-exposure to a pathogen due to Memory B cells.

Active Immunity

Immunity that develops as a result of exposure to a pathogen, leading to the production of antibodies.

Entrance Sites for Pathogens

Include the surface of skin, nasal passages, respiratory system, tear ducts, and the digestive tract.

Defense Mechanisms of the Body

Includes sebum, sweat, mucus, tears, stomach acid, bile, and the normal microbiota, all contributing to pathogen protection.

Past the body's initial defenses

If pathogens get ________ evade phagocytic cells, inflammation, fever, and the complement system, they may trigger the adaptive immune response.

Fevers

Hypothalamus, raising body temperature and constricting blood vessels to enhance immune response and inhibit pathogen growth.

Histamines

Chemicals released during an immune response that increase blood flow and capillary permeability, leading to inflammation. Signs include redness, heat, swelling, and pain; examples include bug bites.

Effects of the Complement System

1. Activates inflammatory response. 2. Acts as opsonin to increase phagocytosis (Opsonization). 3. Activates cascade to trigger MACs (Membrane Attack Complexes) that create large holes in membranes of gram-negative bacteria and enveloped viruses.

Cell Mediated Pathways

APCs present antigen to Helper T cells, activating them. Activated Helper T cells become Effector Helper T Cells (which proliferate and secrete Interleukins to stimulate Cytotoxic T cells and B cells) and some become Memory T Cells (long-lived, dispersed throughout the body for rapid response). Effector Cytotoxic T Cells recognize and destroy infected body cells by releasing perforins.

Humoral Pathway

Involves Interleukins released by Effector Helper T Cells activating B Cells; APC binds to B Cell receptors, leading to proliferation and differentiation into Plasma and Memory B Cells. Plasma Cells secrete antibodies that bind to antigens, while Memory B Cells respond rapidly to subsequent infections by the same pathogen.

MAC

Membrane Attack Complex, a structure formed by the complement system that creates pores in the membranes of target cells, leading to cell lysis.

Types of Antibodies

Immunoglobulins that play crucial roles in immune responses. Examples include: IgA, IgD, IgG, IgE, and IgM.

IgG

The most abundant antibody (~80%), effective against bacteria, viruses, and toxins; involved in the secondary antibody response and can transfer maternal immunity during pregnancy.

IgA

Found in breast milk, tears, nasal fluid, bile, and urine; it plays a critical role in mucosal immunity.

IgM

Involved in primary antibody response; the first antibody produced in response to an infection, known for its role in activating complement.

IgD

Found on the surface of B cells, involved in initiating B cell activation.

IgE

Associated with allergic reactions and responses to parasitic infections.

Memory B cells

Make antibodies without being activated by Helper T cells. They remain in Lymphoid tissues.

Memory T cells

Kill infected body cells without being activated by Helper T cells.