Chapter 7 adaptive immunity Flashcards
adaptive immunity
3rd line of defense. Consist of lymphocytes and antibodies (serum proteins). SLOW
Specific and inducible (lymphocytes and antibodies don’t exist in large #’s until infection), long-lived and systematic and provides long term protection. Has memory.
antigen
molecular targets of antibodies an lymphocytes on surfaces of microbes, cells or tissues. Binds with antibodies or antigen receptors on B and T cells
immunogen
molecule that binds to receptors AND INDUCES IMMUNE RESPONSE`
Hapten
low molecular weight molecules, too small to induce an immune response but if combines with larger molecules will (poisin ivy)
T cells mature in the ______
B Cells mature in the ______
thymus
bone marrow
what is immunocompetent?
Right after leaving primary lymphoid organs b& t cells are immunocompetent (can respond) but haven’t been exposed to antigen so are naïve. They migrate to secondary lymphoid organs (lymph nodes and spleen, tonsils, adenoid). More circulating lymphocytes are T cells than B cells
humoral immunity vs. cellular immunity
antibodies circulating in blood vs effector T cells defend against intracellular pathogens (viruses) and abnormal cells like cancer
cellular diversity
production of B and T cells primarily before birth and throughout life that have the capacity to recognize almost any foreign antigen
clonal selection
after exposure to an antigen it’s processed by a phagocyte, these express the processed antigen on their surfaces and present this to the lymphocytes. Differentiation occurs after a series of other events and occurs in peripheral lymphoid organs. Final products include plasma cells that produce antibody, effector T cells help (helper T) that kill targets (killer T) or regulate immune response (treg), memory B and T cells
Somatic recombination
multiple DNA combinations that can encode BCrs
Development of B lymphocytes
Stem cells in bone exposed to hormones and cytokines that induce proliferation and differentiation into B cells
b) B cell receptor is developed—this is a complex of antibody bound to cell surface involved in intracellular signaling. Role is to recognize antigen and communicate that info to cell’s nucleus
i) BCRs for immunocompetent cells are mIgM with or without IgD antibodies
c) >90% of developing B cells are sent back to bone marrow where they undergo apoptosis due to being autoreactive (in autoimmune disease or hypersensitivities). Also known as clonal deletion or CENTRAL TOLERANCE
d) Peripheral tolerance occurs in tissues (T-regulatory lymphocytes)
development of T lymphocytes
a) Stem cells from bone marrow migrate to thymus where they are driven to gain receptors and undergo cell division (d/t influence of thymic hormones and cytokine IL-7)
b) Exit through blood vessels and lymphatics as immunocompetent T cells and live in the secondary lymphoid organs.
c) Most TCR (t cell receptors) consists of and alpha and beta protein chain and a CD3 signaling molecule.
i) CD4 and CD8—on immature cells are both. Once mature they retain only one or the other.
ii) CD4 develop into t helper cells
iii) Cd8 develop into T-cytotoxic (killer) cells
iv) Central tolerance for T cells occurs in the thymus
if a T cell hold onto CD8 it is a
T-cytotoxic (killer) cells
if a t cell holds onto CD 4 it is a
t helper cells
What is a major histocompatability complex (MHC)?
these present the antigens and can be class 1 or 2
(1) Class 1—on all nucleated cells (except RBCs)—present ENDOGENOUS antigens—recognized by Tc cells
(2) Class 2—only on APCs (macrophages, dendritic cells and B lymphocytes—present EXOGENOUS antigens). –recognized by T helper cells
what are the antigenic presenting cells (APCs)
B cells, macrophages, dendritic cells
APCs have which MHC class
Class 1 & class 2 so can present endogenous & exogenous antigens.
3 intercellular signals that cause clonal selection effector cells to be formed
antigen-specific recognition through TCR or BCR complex, activation of intercellular communication, response to specific groups of cytokines. If missing 1 of these events a protective immune response won’t be produced
What are effector cells
Th, Tc and plasma cells (antibodies)
explain what must happen for a Th cell to be activated and thus to form effector cells
Activation requires 6 steps:
- recognize/bind by TCR on Th
- CD4 on Th of MHC class 2 strengthens binding
- CD3 and CD4 activate intracellular signaling pathways
- adhesion molecules/costim. Signals further activates Th cell (most important is B& protein on APC and CD28 on Th)
- IL1 secreted by APC
- IL2 secreted by Th (without this cell can’t mature into functional helper cell)
Many different types of Th cells. Th1, Th2, Th17 or treg.
what are superantigens?
manipulate APC+Th interaction to detriment of individual. Bind to TCR + MHC2 and activate Th cells–?overproduction of inflammatory cytokines and causes systemic inflammatory reaction like fever, low bp and possibly shock. Ex. Staph aureus and strep pyogenes.
What are Tc cells?
cytotoxic T cells Tc cell TCR recognizes antigen presented by MHC class1 molecule on surface of APC, binds to CD8 on Tc cell, activates signals on Tc cell
iTc lmphocytes—adheres to antigen presented by MHC 1 and CD8
Induces apoptosis
Cell mediated immunity
B cell clonal selection
(i) Immunocompetent B cell is also an APC and expresses surgace mIgM and mIgD BCRs.
(ii) BCR can react with antigens that haven’t been processed (unlike T cells). Also has surface CD21 which is a receptor for opsonins. BCR+CD21activated B cell. They have MHC class 1 but present antigens on MHC class 2 to activate Th cells.
(iii) Plasma cells are activated B cells that produce antibodies and can detect the identical antigen as the BCR.
memory cells
B & T cells differentiate into long lived cells. Remain inactive until exposure. These will become new plasma cells or effector T without the cell interactions described as above.
