Chapter 1: Overview of the Immune System

Overview of Humoral (B-Cell) and Cellular (T-Cell) Branches of Immunity:

- B-Cells produce antibodies, soluble version of their receptor protein, which will then bind to foreign protein to flag them for destruction. -T-Cells use T-cell receptors to sense antigen: -Secrete compounds to aid other WBCs (B-Cells) and -Destroy infected host cells

Compare and contrast innate immunity and adaptive immunity?

-Innate responses are rapid but less pathogen-specific, using inherited recognition molecules and phagocyting cells. -Adaptive responses are slower (taking days to develop) but highly specialized to the pathogen, and rely on randomly-generated recognition receptors made by B and T-cells. -Both, Innate and adaptive immunity operates cooperatively; activation of the innate immune response produces signals that are required to stimulate and direct the behavior of adaptive immune pathways.

Examples of physical barrier of the body:

-Skin -Mucous in Membrane -Acidity , i.e Sweat -Antimicrobial proteins secreted by epithelial cells

Name the three unique pathways that are specific for different types of pathogens:

1. Cytotoxic T-Cells kill infected host cells 2. T-Helper cells assist other immune cells 3. Antibodies, secreted via B-Cells, fight extracellular (outside of the cell) infection.

Name three recognition molecules:

1. Membrane-Bound Receptors 2. Soluble Receptors 3. Secreted Recognition Molecules

Collaboration between Innate and Adaptive Immunity in Resolving an Infection Step(s):

1. Pathogens entire body through mucosal surfaces. After breaching epithelial cell barriers, 2. Pathogen is detected by resident phagocytic cell (yellow) and innate immunity response begins. Responding phagocytic cells undergo changes that allow them to fight infection locally via releasing: -Antimicrobial compounds -Cytokines -Chemokines (all shown in blk dots), all 3 will help recruit other immune cells to the site of inflammation. 3. Pathogen and phagocytic cells, migrate to the lymphatic vessels toward the secondary lymphoid structures--the lymph nodes 4. Where they intersect with lymphocytes entering from the blood. 5. Adaptive immunity is initiated in secondary lymphoid structures, where T-helper cells (TH blue), T cytotoxic cells (TC red), and B-cells (B green) with appropriate receptor specificity bind pathogen and are clonally selected. 6. These specialized T and B cells, along with their products aka antibodies migrate out of the lymph nodes and into the bloodstream pumped by the heart through the body. 7. As they identify areas of infection ( from the earlier site of inflammation) they exit the blood vessels and 8. Migrate toward the infection, where they can help label and destroy any remaining pathogen (the effector phase). Residual long-term memory T and B cells take up residence in various locations in the body, where if the pathogen is encountered again it can initiate a more rapid and antigen-specific secondary response.

The four major categories of human pathogens:

1. Viruses 2. Bacteria 3. Fungi 4. Parasites *(Very Bad For People)

B-Lymphocytes (B-Cells)

A WBC that matures in the bone marrow and produces antibodies. It is part of humoral immunity.

T-Lymphocytes (T-Cells)

A WBC that matures in the thymus, it can directly eradicate infectious agent, and aid cells in their work. It is part of cell-mediated immunity.

Generation Diversity

A diverse repertoire of antigen-binding receptors on B or T lymphocytes results in a cell pop. that can respond to any antigen type. Accomplished by rearranging DNA expressed in antigen receptors, results in unique receptors for each B and T-Cell, will not be passed to offspring.

What are booster shots used for?

A second or third episode of exposure to the antigen, to refine the responding lymphocyte population, in order to provide protection against the real pathogen.

T-Helper Cell

A specialized T-Cell that guides the behavior of other immune cells, including B-cells, and is pivotal for selecting the pathway taken by the immune response. For example, HIV infects T-Helper cells and missing directional cues from T-Helper causes problems w/ fighting off infections.

Secondary response

All subsequent encounters with the same antigen or pathogen.

Antigen

Any substance that elicits a specific response by B or T-Lymphocytes. For example, a B-cell can be triggered to proliferate to secrete many copies of antibodies, once it has been selected by antigen binding.

Memory cells

B and T-lymphocytes trained during the primary response, are re-enlisted to fight again. Continuing to learn and improve their eradication strategy for each encounter w/ the same antigen. Will save the strategy, not the vaccine, for later reference during repeat encounters w/ same antigen

Clonal Selection

B or T-lymphocytes express many copies of one membrane receptor, the receptor specificity is determined prior to antigen exposure, and is specific to one distinct antigen.

Pathogen-Association Molecular Patterns (PAMPs)

Common chemical structures on pathogens, that allow for the immune system to recognize; Used for pathogen profiling.

Antibodies

Derived from B-Cells. Active molecules in the immunoglobulin serum, contained in body fluids and participate in humoral immunity.

Primary response

First encounter with foreign antigen, during which key lymphocytes will be used to eradicate the pathogen are clonally selected, honed, and enlisted to resolve the infection.

Tolerance

Hallmark of the immune response, relies on self/non-self discrimination. Antigen receptors on B and T-Cells must first pass a test of nonresponsiveness against the host, this ensures that the host always knows the difference between self/non-self.

Passive Immunity

Immune protection transferred between individuals, w/o receiving individuals making his/her own immune response against the pathogen. An example: Newborn infants benefit from passive immunity by the presence of maternal antibodies.

Where does the transition from innate to adaptive immunity occur?

In the lymph nodes, which are specialized organs in the immune system. Through one route, the fluid bathing our tissues is funneled to and filtered through sieve-like structures before it is returned to the blood.

Humoral Immunity

Involves combating pathogens via antibodies, which are produced by B cells and are found in bodily fluids. Antibodies can be transferred to individuals aka passive immune protection.

Cell-mediated Immunity

Involves pathogen-specific T-Lymphocytes, that can act directly to eradicate the infectious agent and also aid other cells in their work.

Active Immunity

Long-lived protection comes from memory cells, which provide protection for years after the initial exposure.

Cytokines

Messenger protein, soluble or membrane-bound, these messengers bind to receptors on responding cells, inducing intracellular signaling cascades, results in: -activation -proliferation, and -differentiation *sometimes causes mediated changes in gene transcription --> induce new functions in the target cell. -Just like Chemokines will draw fluid to the site of infection.

Why must a new flu vaccine be made every year?

New mutations of the flu appear every year that are different from the previous year's flu. Flu vaccines are predictions of the genotypes likely to be encountered the next season.

Hypersensitivity Reactions

Overly zealous attacks on common benign antigens (pollen, food or animal dander). Examples: -Allergies -Asthma

Complement

Part of innate immunity, includes pre-existing serum proteins. Will bind common pathogen-associated structures and initiate a cascade of labeling and destruction events. Are the first line of defense.

Why is adaptive immunity slower?

Partly because fewer cells have the perfect receptor for the job, recall antigen-specific T and B-cell receptors are generated via DNA rearrangement. Also it relies on prior encounter and "categorizing" of antigens via the innate process.

B cell receptor

Recognition molecules on the surface of B lymphocytes, are classified as antibodies in their secreted form.

Chemokines

Soluble signals, have chemotactic activity, meaning they recruit specific cells to the site--leave molecular breadcrumbs. -Just like Cytokines will draw fluid to the site of infection.

Areas of the body that are "off limits" for the immune system?

The central nervous system and the eye are "off-limits" because the immune system can do more harm than the pathogen.

Innate Immunity

The first form of immunity, present before exposure and effective since birth. A Primitive and highly conserved response system, that includes: -physical, -chemical barriers and -DNA-encoded receptors aka PRRs (pattern recognition receptors) quick and dirty response: -Rapid recognition -Phagocytosis -Complement aka pre-existing serum proteins

Adaptive Immunity

The second form of immunity attuned to subtle molecular differences. Relies on: -B-Lymphocytes -T-Lymphocytes It takes longer to come on board but is more antigen-specific. Typically, the response against a pathogen is 5-6 days.

Immunologic memory

Unique attribute of the adaptive arm to respond much more swiftly and with greater efficiency during a second exposure to the same pathogen.

Pattern Recognition Receptors (PRRs)

WBCs express a variety of receptors (aka PRRs), will recognize pathogens via PAMPs, i.e. sugar residues on bacteria

Phagocytes

White blood cells that ingest microorganisms and other foreign material

Lymphocyte

White blood cells, responsible for both humoral (B-Cells) and cell-mediated immunity (T-Cells).

Immunity

a state of protection from infectious diseases

What is the principle behind vaccination?

that exposure to safe forms of an infectious agent can result in future protection against the more dangerous form of the infectious agent

Herd Immunity

the resistance of the disease to where a large proportion of the population is immune

Inoculate

to introduce a microorganism, serum, or vaccine into an organism in order to increase immunity to illness

Attenuated

weakened pathogen/ strain administered as a vaccine to provide immunity against the disease