Topic 4: Adaptive Immunity Flashcards
What are the three types of T lymphocytes
- helper cells
- regulatory cells
- cytotoxic cells
What is adaptive immunity?
immune response mediated by B and T lymphocytes to infectious agents and noninfectious molecules
What are the differences between innate and adaptive immunity
Innate
- detects common microbial structures
- receptors are encoded in the germline
- same response upon repeat exposure
- immediate response
Adaptive
- detects vast repertoire of molecules -> can be very specific
- receptors generated by somatic recombination
- improved adapted response to repeat exposure
- delayed response
What are antigens
- a foreign molecule from a pathogen
What types of antigens are recognized by B cells
- proteins
- lipopolysaccharides
- lipids
- nucleic acids
What types of antigens are recognized by T cells
- peptides derived from proteins
How do T and B cells differ in how they associate with antigens
- T cells require antigen presentation be dedicated antigen presenting cells
- B cells directly recognize its cognate antigen
What are the two forms of adaptive immunity
- humoral immunity and cellular immunity
What is humoral immunity
-directed against extracellular microbes
- mediated by B lymphocytes
- B lymphocytes secrete antibodies that neutralize and eliminate microbes and microbial toxins
What is cellular immunity
- directed against intracellular microbes
- mediated by T lymphocytes
- T lymphocytes activate phagocytes and lymphocytes or kill infected host cells
What is the function of Humoral Immunity
use B lymphocytes to block infection and eliminate extracellular microbes
What is the function of cell-mediated immunity by helper t cells
activate macrophages to kill phagocytosed microbes
What is the function of cell-mediated immunity by cytolytic t cells
kill infected cells and eliminate reservoirs of infection
What are the phases of the immune response?
- Recognition
- Activation
- Effector Phase
- Decline
- Memory
What is the Recognition phase
naive lymphocytes recognize corresponding antigens
What is the Activation phase
lymphocytes differentiate and start clonal expansion
What does activation require?
activation requires two signals, antigen receptor binds antigen (signal 1). Microbial or innate immune signals are also required for lymphocyte activation; can be cytokines, chemokines
What is clonal expansion
- when a BCR or TCR dectects an antigen the B cell or T cell undergoes multiple rounds of cell division, thereby expanding. Each daughter is identical to the parent cell
What is the effector phase?
differentiated lymphocytes initiate microbial elimination
What is the decline phase
after microbial elimination the signal for lymphocyte activation disappears. Most of the cells activated by antigen die by a process of programmed cell death (apoptosis)
What is the memory phase
remaining cells become memory lymphocytes, which can result in stronger responses to subsequent challenges with the same antigen
What are B lymphocytes
- each BCR recognizes a distinct microbial 3-dimensional structure
- naive B cells are activated by antigens and another second signal
- activation leads to proliferation and diffferentation into effector cells that secrete antibodies. BCR productions is now modified that BCR is secreted as an antibody
What is an antibody
- released into circulation and mucosal fluids by B cells upon infection
- neutralizes microbes and microbial toxins
- stops microbes from gaining access to host cells
- does not have access to intracellular microbes
What are antigen presenting cells
T lymphocytes require antigen presentation from antigen presenting cells (APC). APCs capture, process and present antigens to T lymphocytes in lymphoid tissues
What are the two types of T lymphocytes
- CD4 helper T cells
- CD8 cytolytic T cells
What are CD4+ helper T cells
- detect antigens presented by professional antigen presenting cells.
- secrete cytokines to activate other components of the immune response (macrophages)
- have class II MHC that help in presentation of antigen to helper T cells
What are CD8+ cytolytic T cells
detect microbial antigens presented by all nucleated cells and destroy the presenting cells
- have class I MHC that present cystolic antigen to cytolytic T lymphocytes
What is the peripheral lymphoid organs
- lymph nodes
- spleen
- mucosal and cutaneous lymphoid tissues
- concentrate antigens and lymphocytes to optimize interactions
What is the lymphatic system
- a network that transports fluids from tissues through lymph nodes and ultimately to the circulatory system (initially to veins)
- excess interstitial fluid is collected by the lymphatic system and is processed by lymph nodes prior to being deposited into the circulatory system
- lymphatic system is not closed and has no central pump
How are T lymphocytes activated in the lymph nodes
- APCs drain from peripheral tissues into lymph nodes
- T lymphocytes enter lymph nodes
- APCs activate T lymphocytes
- Lymphocytes exit lymph nodes and enter circulation, then exit circulation into inflamed tissue where they mediate microbial destruction
