Overview of the Immune System and Its Functions

Immune System

An organism's defense system against pathogens.

Innate Immune System

The first line of cellular defense that generates a rapid, nonspecific immune response.

External Immunity

Includes physical and chemical barriers that prevent pathogen entry.

Physical barriers

Skin and organ mucosal layers that prevent pathogen entry.

Chemical barriers

Substances like stomach acid and lysozymes that kill microbes.

Leukocytes

White blood cells that are important molecules of the immune system.

Cytokines

Chemical signaling molecules used in the immune response for cell-cell communication.

Phagocytic leukocytes

Leukocytes that engulf foreign particles, bacteria, and dead cells via phagocytosis.

Neutrophils

Leukocytes that function in the destruction of pathogens in infected tissues.

Eosinophils

Leukocytes that surround and destroy multicellular parasites.

Monocytes

Leukocytes that circulate in blood until they move into tissues and develop into macrophages.

Basophils

Leukocytes that release histamine in the inflammatory response.

Natural Killer (NK) Cells

Leukocytes that attack abnormal body cells, either tumors or pathogen-infected cells.

Macrophages

In tissues, they phagocytize cell debris and pathogens and are derived from monocytes.

Dendritic cells

Cells that ingest pathogens and stimulate the acquired immune response.

Complement System

Contains complement proteins that circulate the body and assist in activating the immune response.

Relative abundance of the Leukocytes

Neutrophils > Lymphocytes > Monocytes > Eosinophils.

Toll-like Receptors (TLRs)

Critical to innate immunity; they recognize molecular patterns that many pathogens have.

Adaptive Immune System

The specific, third, and last line of immune defense that develops after the body has been attacked.

Antigens

Specific targets of the immune response in the adaptive immune system.

Epitopes

An epitope is a specific part of an antigen to which an antibody binds

Antibodies

Proteins that bind to a specific antigen they recognize

Lymphocyte

Primary cells of the adaptive immune response & originate in the bone marrow and concentrate in lymphatic tissue such as lymph nodes, thymus gland, and spleen

B Cells

B cells originate and mature in the bone marrow

T Cells

T cells originate in the bone marrow but mature in the thymus, and have antigen receptors

Clonal Selection

When a foreign antigen activates a B cell, proliferation (or expansion of the B cell population) occurs, thus forming daughter B cells

Plasma Cells

B cells that circulate in the blood and release specific free antibodies that dispose of antigens by agglutination, inactivation, opsonization, and lysis

Memory Cells

Long-lived B cells that store memory of an antigen they have encountered, proliferate, and respond quickly to eliminate subsequent invasion by the same antigen

Cytotoxic T cells

Killer T cells that destroy by releasing perforin protein and via lysis

Helper T cells

Stimulate activation of B cells, cytotoxic T cells, and suppressor T cells

Suppressor T cells

Play a negative feedback role in the immune system

Memory T cells

Similar in function to Memory B cells

Major Histocompatibility Complex - MHC

A collection of glycoproteins that exists on membranes of all body cells

Active Immunity

Acquired after direct exposure to an infection/vaccine

Natural Active Immunity

Antibodies made after exposure to pathogen

Artificial Active Immunity

Antibodies made after getting a vaccine

Passive Immunity

Acquired from external sources

Natural Passive Immunity

Antibodies transferred from mother to baby

Artificial Passive Immunity

Antibodies given to you via a serum injection

Cell-Mediated Response

Occurs when an infected cell is recognized and bound by a T-cell

Antigen Presenting Cells

The three types of APCs are macrophages, dendritic cells, and B cells

Vaccines

Build immunity to a specific part of a pathogen by placing a weak end or dead form of the pathogen via a preventative technique

Antibiotics

Facilitate human immune responses by killing or inhibiting the growth of bacteria

Disulfide bridge

The two heavy chains are linked to two light chains by disulfide bonds