BIOM-3070 Week 5 - Immunity

Innate immunity

The body's nonspecific defenses, including the first line of defense (barriers) and the second line of defense (cells, chemicals, and processes).

First line of defense

Structures, chemicals, and processes that work to prevent pathogens from entering the body, including the skin and mucous membranes.

Epidermis

Multiple layers of tightly packed cells that few pathogens can penetrate. Shedding of dead skin cells removes microorganisms, and epidermal dendritic cells phagocytize pathogens.

Dermis

Collagen fibers help skin resist abrasions that could introduce microorganisms.

Sebum

Oil secreted by sebaceous (oil) glands. It helps keep skin pliable and less likely to break or tear, and lowers skin pH to a level inhibitory to many bacteria.

Perspiration

Secreted by sweat glands. Salt inhibits growth of pathogens, and antimicrobial peptides act against microorganisms.

Lysozyme

Destroys the cell wall of bacteria.

Mucous membranes

Line all body cavities open to the environment. They have two layers: an epithelium and a deeper connective layer that supports it.

Mucous membrane epithelium

Thin outer covering, tightly packed to prevent entry of many pathogens. Continual shedding of cells carries away microorganisms, and dendritic cells below the epithelium phagocytize pathogens.

Goblet and ciliated columnar cells

Help remove invaders from mucous membranes.

Microbiome

Competes with potential pathogens by consuming nutrients, creating an environment unfavorable to other microorganisms, preventing pathogens from attaching to host cells, and generating antimicrobial compounds. It also provides vitamins to the host and stimulates the second line of defense.

Microbial antagonism

The microbiome making it hard for pathogens to compete, attach, and grow.

Second line of defense

Operates when pathogens penetrate the skin or mucous membranes. It is composed of cells, antimicrobial chemicals, and processes, many contained in or originating in the blood.

Plasma

Mostly water containing electrolytes, dissolved gases, nutrients, and proteins. Complement proteins and antibodies are also found in plasma.

Serum

The fluid remaining when clotting factors are removed from plasma.

Iron-binding compounds

Found in plasma. Iron is needed for metabolism, and some microbes produce proteins that bind iron.

Formed elements

Cells and cell fragments in plasma: erythrocytes, platelets, and leukocytes.

Erythrocytes

Carry oxygen and carbon dioxide in the blood.

Platelets

Involved in blood clotting.

Leukocytes

Defend the body against invaders. They are divided into granulocytes (innate) and agranulocytes (adaptive).

Differential white blood cell count

Can signal disease. Increased eosinophils indicate allergies or parasitic worm infection. Bacterial diseases often show increased leukocytes and neutrophils, while viral infections show increased lymphocytes.

Phagocytes

Cells capable of phagocytosis: neutrophils, eosinophils, and monocytes.

Phagocytosis stages

Six stages: chemotaxis, adhesion, ingestion, maturation, killing, and elimination.

Toll-like receptors (TLRs)

Integral membrane proteins produced by phagocytic cells. They bind pathogen-associated molecular patterns (PAMPs) and initiate defensive responses, secretion of inflammatory mediators, and stimulation of the adaptive immune response.

PAMPs

Pathogen-associated molecular patterns bound by Toll-like receptors.

Apoptosis

Programmed cell death triggered as a nonspecific chemical defense.

Inflammation

A nonspecific response to tissue damage, characterized by redness, heat, swelling, and pain. Two types: acute and chronic.

Acute inflammation

Develops quickly and is short lived. It is typically beneficial and important in the second line of defense.

Chronic inflammation

Long-lasting inflammation in which damage to tissues can cause disease.

Vasodilation in inflammation

Produces redness and localized heat. It is triggered by bradykinins, prostaglandins, leukotrienes, and histamine, and delivers blood clotting proteins to the site of injury.

Migration of phagocytes

Neutrophils and monocytes are delivered to the infection site, recruited by chemotactic factors. They attach to receptors on blood vessels, squeeze between cells of the vessel wall, and enter the site. Delivery of nutrients and oxygen facilitates tissue repair.

Fever

A body temperature over 37 degrees C. It results when pyrogens trigger the hypothalamus to increase the body's core temperature.

Pyrogens

Include bacterial toxins, cytoplasmic contents of bacteria released by lysis, antibody-antigen complexes, and pyrogens released by phagocytes that have phagocytized bacteria.

Adaptive immunity

The body's ability to recognize and defend itself against distinct invaders and their products.

Five attributes of adaptive immunity

Inducibility, clonality, unresponsiveness to self, memory, and specificity.

B lymphocytes (B cells)

Mature in the bone marrow. Their major function is the secretion of antibodies, and they are found primarily in the spleen, lymph nodes, and MALT.

T lymphocytes (T cells)

Mature in the thymus. They are produced in the bone marrow, circulate in the lymph and blood, and migrate to the lymph nodes, spleen, and Peyer's patches.

Cell-mediated immune response

One of two types of adaptive immune responses, driven by T cells.

Antibody (humoral) immune response

One of two types of adaptive immune responses, driven by antibodies.

Antigen

A molecule the body recognizes as foreign and worthy of attack, recognized by three-dimensional regions called epitopes. Large foreign macromolecules make the best antigens.

Epitope

A three-dimensional region on an antigen that is recognized by the immune system.

Exogenous antigens

Include toxins and other components of microbial cell walls, membranes, flagella, and pili.

Endogenous antigens

Produced by microbes that reproduce inside a body's cells.

Autoantigens

Derived from normal cellular processes, for example insulin and myelin.

Major histocompatibility complex (MHC)

Glycoproteins found in the membranes of most vertebrate cells that hold and position antigenic epitopes for presentation to immune cells. First identified in graft patients and important in tissue graft compatibility.

Antigen-binding groove

Antigens bind in the antigen-binding groove of MHC molecules.

MHC class I

Present on all cells except red blood cells.

MHC class II

Present on antigen-presenting cells (APCs), including macrophages and dendritic cells.

Antigen-presenting cells (APCs)

Include macrophages and dendritic cells. They display epitopes on MHC class II proteins.

Antigen processing

Antigens are processed for MHC proteins to display epitopes, with different processes for endogenous and exogenous antigens.

T cell receptor (TCR)

Found on the T cell cytoplasmic membrane. TCRs do not recognize epitopes directly; they only bind epitopes associated with an MHC protein.

T cell targets

T cells act primarily against cells that harbor intracellular pathogens and against body cells that produce abnormal cell-surface proteins, for example cancer cells.

Cytotoxic T lymphocyte

Directly kills other cells.

Helper T lymphocyte

Helps regulate B cells and cytotoxic T cells. Includes type 1 and type 2 helper T cells.

Regulatory T lymphocyte

Represses adaptive immune responses.

Clonal deletion of T cells

The body eliminates self-reactive lymphocytes, which undergo apoptosis, so immune responses are not directed against autoantigens.

B cell receptor (BCR)

Each B lymphocyte has multiple copies of a single BCR, with two variable regions forming the antigen-binding sites. Each BCR recognizes only one epitope.

RAG enzyme

Combines different variable region gene segments to generate antibody diversity.

Plasma cells

Activated B cells that secrete antibodies. Antibodies are immunoglobulins with antigen-binding sites and specificity identical to the BCR of the activated B cell.

Antibody functions

Neutralization, opsonization, agglutination, and antibody-dependent cellular cytotoxicity (ADCC).

IgM

The first antibody produced.

IgG

The most common and longest-lasting antibody.

IgA

Associated with body secretions.

IgE

Involved in response to parasitic infections and allergies.

IgD

Exact function is not known.