Exam 4 Flashcards
Describe an antigen
Molecules that can be seen and identified by the immune system.
Describe an epitope
The actual binding site of the immunogen is so specific it only binds this portion of the molecule
Describe what the MHC is
Major histocompatibility complex: one of the set of genes that codes for human cell markers or receptors.
Gives rise to a series of glycoproteins found on all cells except RBC.
Also known as the human leukocyte antigen (HLA) system.
These markers play a vital role in recognition of self by the immune system and in rejections of foreign tissue.
What are the 3 major functions of activated T cells
Helper T cells: activate macrophages, assist B-cell processes, and help activate cytotoxic T cells.
Regulatory T cells: control T-cell response by secreting anti-inflammatory cytokines or preventing proliferation
Cytotoxic T cells: lead to the destruction of infected host cells and other “foreign” cells
Describe the two most common functions of activated B-cells
Plasma cells: release antibodies into the tissue and the blood
Antibodies: attach to the antigen for which they are specific, and the antigen is marked for destruction or neutralization.
List the function of CD3 receptors and where they’re found
Surround T-cell receptors and assist in binding
List the function of CD4 receptors and where they’re found
Accessory receptor proteins that helps the T-cell receptor bind to MCH II molecules
List the function of CD8 receptors and where they’re found
found on cytotoxic T-cells and helps bind MCH I molecules (kills infected self)
Contrast B and T cells
B-cells: develop in the bone marrow. immunoglobulin is the specific surface marker, low numbers circulating in the blood, b-cell receptor (immunoglobulin), distribution in lymphatic organs is in cortex (follicles) doesn’t require an antigen presented produces plasma cells and memory cells, general functions produces antibodies to inactivate, neutralize, target antigens.
T-cells: develop in the thymus, specific surface markers are t-cell receptor & several CD molecules, high numbers in the blood stream, receptor for antigens in the T-cell receptor, distribution in lymphatic organs is in paracortical sites (interior to the follicles) needs an antigen presented, produces several types of T-cells and memory cells general functions cells activated to help other immune cells; suppress or kill abnormal cells; mediate hypersensitivity; synthesize cytokines
Describe the structure of immunoglobulin
Large glycoprotein molecules that serve as the antigen receptors of B-cells. Serves as antibodies when secreted.
Looks like a font Y has pockets in the ends of forks of the molecules that can be highly variable in shape to fit a wide range of antigens, has areas of extreme versatility from one clone to another. Has light chain (right top) heavy chains (right bottom) Variable region (top left)
Describe the structure of an antibody
every antibody is unique
Describe the process that results in the incredible diversity of IG/antibody and T-cell receptor diversity and specificity
Diversity is generated by rearrangement of gene segments that code for antigen receptors on T and B cells every possible recombination occurs, leading to a huge assortment of lymphocytes
It is estimated that each human produces antibodies with 10 trillion different specificities
What is clonal selection
The mechanism by which the exactly correct B or T cell is activated by any incoming antigen. Lymphocyte specificity is preprogrammed, existing in the genetic makeup before an antigen has ever entered the tissues. Each genetically distinct lymphocyte expresses only a single specificity and can react to that chemical epitope
What is clonal expansion
The rapid multiplication of B or T cell clones after activation by an antigen
What is clonal deletion
The process by which any such clones are destroyed during development
Describe the characteristics of a “good” antigen
a) their chemical composition (complex, not repeated); b) their context (meaning what types of cytokines are present); and c) their size:
Define Hapten
Small foreign molecules that are too small by themselves to elicit an immune response
If this incomplete molecule is linked to a larger carrier molecule, the combination develops immunogenicity
The hapten serves as the epitope
Describe what superantigens are and what can result in people who react to them
Bacterial toxins that are potent stimuli for T cells
Activate T cells at a rate 100 times greater than ordinary antigens
The result can be an overwhelming release of cytokines and cell death
Toxic shock syndrome and certain autoimmune diseases are associated with superantigens
Describe the process of antigen presentation by dendritic cells, including the MHC and CD proteins involved in the process, what they present to, and the result of presentation
In most immune reactions, the antigen must be formally presented to lymphocytes by antigen-presenting cells (APCs)
Examples of APCs:
Macrophages
B cells
Dendritic cells (usually these)
After processing is complete, the antigen is bound to the MHC receptor and moved to the surface of the APC so it will be readily accessible to T lymphocytes
Know whether all antigens must use APCs to lead to B-cell activation
Most antigens must be presented first to T cells, even though they will eventually activate both the T-cell and B-cell systems
T-cell-independent antigens: antigens that can trigger B cells directly without APCs or T helper cell
Describe the process of B cell activation
a precomitted B cell binds to the epitope of the receptor
The anitgen is endocytosed by the B cell and degraded into smaller pieces and bound to the MHC-II receptors on the surface of the B cell. For most B-cells to become functional, the must interact with an already active helper T-cell that bears receptors for antigen from the same microbe. This T cell has also been activated by an APC. The two cells enlarge in linked recognition, in which the NHC-II receptor bearing antigen on the B-cell binds to the T-cell antigen receptor, the CD3 Molecule, and the CD4 molecule on the T-cell. The combination of these stimuli on the membrane receptors causes a signal to be transmitted internally to the B-cell nucleus. This event triggers B-cell activation. The B-cell now differentiates into 3 types of B-cells: plasma cells, memory cells, and regulatory cells. Each of the 3 cells expand it’s population. Plasma cells are short lived factories for antibodies of the same specificity as the original B-cell. Memory cells seed the lymphatic circulation, ready for encounters with the same antigens. Regulatory cells proliferate and secrete IL-10 to regulate T-cell response.
List the 6 different functions of an antigen
Opsonization: a process that makes microbes readily recognized by phagocytes, which dispose of them.
Neutralization: Anitbodies fill the surface receptors on the virus or the active site on a microbial enzyme to prevent it from attaching normally.
Agglutinate: the result of antigens cross-linking their cells into large clumps, which renders the antigen immobile and enhances their phagocytosis.
Complement: the interaction of an antibody w/ complement can result in specific rupturing of cells in some viruses.
Antitoxin: a special type of antibody that neutralizes bacterial toxins.
Define titer
the concentration of an anitbody
Describe the pattern of primary and secondary immune system response to antigen in terms of titer over time
In the primary response after the latent period there is an increase of the serum titer to a plateau then tapers off to a low level after weeks and months.
In the secondary response the titer is greatly increased over the primary response.
