Lymphoid Flashcards
Body defense mechanisms
Physical/biochemical barriers, innate immunity, and adaptive immunity
Physical barriers
First line of defense. Skin, ciliary action, fluid movement, normal flora.
Biochemical barriers
First line of defense. Tears, saliva, mucus, stomach acidity, spermine.
Innate immunity
Non-specific immunity that prevents infection or penetration of the body. It lacks immunologic memory and the responses remain unchanged despite encountering a pathogen. Cells involved are mastocytes, granulocytes and agranulocytes.
Natural killer cells
Lymphocyte that contribute to the innate immunity by destroying unhealthy host cells. They lack CD3. CD4. and CD8 surface markers, don’t require antigen processing or MHC recognition, don’t have immunologic memory, and they can kill target cells coated with IgG.
*Surgery or other trauma like experiences reduces there NK cell count.
Acquired immunity
Specific immunity that protects the internal environment of the body by producing specific responses to antigens. 3 characteristics are specificity, diversity, and memory.
Antigen
Substances typically foreign to the host (Ex/microorganisms)
Antigen recognition
Component of adaptive immunity where a lymphocyte must recognize and distinguish non-self vs. self.
Immune response
Component of adaptive immunity. It is the inactivation/elimination of foreign antigens such as, microorganisms, foreign material, cancer cells, and organ transplants.
Antigen encounter
Antigen recognition is enhanced by the circulation and recirculation of lymphocytes through the tissues.
Antigen presenting cells (APC)
Cells found in most tissues that process antigens and present them at their cell surface for T lymphocyte recognition. These include macrophages, dendritic cells, B lymphocytes and Langerhans cells. Associated with MHC-II
B cell lymphocytes
Humoral immunity cells. They are antibody forming cells of the lymphoid system and provide indirect antigen recognition. They differentiate into plasma cells which secrete antibodies. They undergo differentiation in the fetal liver and bone marrow.
T cell lymphocytes
They are the primary effector cells of cell mediated immunity and immunoregulation. They provide recognition though T cell receptors (TCR) and the MHC-I molecules on the surface. They originate in the thymus.
Anamnestic response
Memory cell defense for future exposures to same antigen. A secondary anamnestic response occurs after the primary response, where the expanded population of memory cells allows for a greater specific response upon re‑exposure to the antigen.
Memory cells
They provide an expanded population of cells which retain ability to divide and respond if exposed to the same antigen. Differentiated from B cells.
Antibody (Immunoglobulins)
Proteins which interact specifically with an antigen. Antibody can be found in serum, tissue fluids, and secretions. They contain 2 pairs of identical light chains and heavy chains connected by disulfide bonds, each one a polypeptide with a variable region and a constant region.
IgG
Activates phagocytosis and neutralizes antigens. Only Ig that can cross the placenta. Located in the blood and lymph intestinal fluid. Most abundant class of Ig.
IgM
They are the 1st antibodies produced in an initial immune response. Located on the surface of B lymphocytes. It has a pentamer structure which is confined intravascular spaces.
IgD
Acts as receptor to antigens that trigger B cell activation
IgE
Participates in allergy response and lyses parasitic worms. Located on the cell membrane surface of mast cells and basophils
IgA
Main Ig found in secretions & mucosal fluids (GI and respiratory tract) because they protect the surface from these fluids by resisting proteolysis.
Opsonization
Binding of antibodies to a microorganism facilitates phagocytosis
Agglutination
Antibodies bind to antigens forming aggregates and reducing the number of free antigens
Neutralization
Binding of an antibody to a microorganism blocks their adhesion to cells and inactivates toxins
Cytotoxicity
Antibodies adhere to the surface of worms (pathogens) and stimulate the release of cells from the immune system (eosinophils and macrophages). This induces them to release chemical agents to destroy the pathogen.
Complement activation
Antibody binding to the initial protein of the complement system triggers the complement cascade which produces the membrane attack complex. This complex forms transmembrane channels and cause cell lysis on a pathogen.
Cytokines (Lymphokines)
Polypeptide mediators which are involved with the production and regulation of the immune response. They amplify the response to an antigen non-specifically. Major types include: Interleukins, chemokines, interferons, and colony stimulating factors
3 types of T cells
Cytotoxic (CTL), helper, and memory T cells
T cell receptors (TCR)
Surface receptors uniquely specific for antigen. They ONLY recognize processed antigens if it is incorporated with MHC molecules.
Major histocompatibility complex (MHC) molecules
Special integral membrane molecules that recognize self from non-self cells. Strictly associated with TCR.
MHC-I
Present on all cells and interacts with CD8+ T cells. Does not pass through endosome/lysosome vesicles (Ex/ viruses).
MHC-II
Present on antigen presenting cells and interact with CD4+ T cells. They pass through endosome/lysosome vesicles (Ex/ phagocytosis)
Helper T cells (CD4+)
General inducers of effector cells for cell mediated and humoral immunity. They help to produce memory B cells and plasma cells. They are associated with MHC-II molecules and secrete cytokines.
Cytotoxic T cells (CD8+)
Kill target cells by releasing perforins, inducing apoptosis (fas induction), and releasing granzymes. They are associated with MHC-I molecules.
Perforins
Protein that targets a cell’s membrane.
Granzymes
Serine proteases that kill intracellular microbes directly through apoptosis
