3 Microbiology: Adaptive (Specific, Acquired) Immunity (not done) Flashcards
Adaptive immune responses are generated by what?
clonal selection of lymphocytes.
In the earliest stages of infection, innate responses do what?
predominate, but later the lymphocytes start to generate adaptive immune responses.
Adaptive immune responses display what four characteristic features?
Antigenic specificity
Diversity
Immunologic memory
Self/nonself recognition
Describe Antigenic specificity
Lymphocytes can distinguish subtle differences between two molecules that differ by only a single amino acid.
Describe Diversity
The immune system is capable of generating tremendous diversity in its recognition molecules, allowing it to specifically recognize billions of uniquely different structures on foreign antigens.
Describe Immunologic memory
Once a lymphocyte has recognized and responded to an antigen, it exhibits immunologic memory, ie, it also “remembers” the pathogen, and mounts a more effective and rapid response should the individual or animal become reinfected with the same pathogen at a later date.
Describe Self/nonself recognition
The immune system normally responds only to foreign antigens indicating that it is capable of self/nonself recognition.
What are antigens?
are substances capable of inducing a specific immune response.
An antigen is the initiator and driving force for all adaptive immune responses.
The immune system has evolved to do what?
to recognize antigens, destroy them and eliminate the source of their production—bacteria, virally infected cells, etc.
When antigen is eliminated, immune responses switch off.
Antigens are generally very large and complex, therefore they are not what?
they are not recognized in their entirety by lymphocytes.
Instead, both B and T lymphocytes recognize discrete sites on the antigen called antigenic determinants or epitopes.
What are Epitopes?
are the immunologically active regions on a complex antigen, the regions that actually bind to B cell receptors and antibodies or T cell receptors.
What is polyvalent?
A particular antigen can have several different epitopes
What is multivalent?
A particular antigen can have repeated epitopes
Why are Lymphocytes central to all adaptive immune responses?
they specifically recognize individual pathogens.
In addition to lymphocytes what also play an essential role in the adaptive immune response?
accessory cells such as antigen-presenting cells
Lymphocytes and accessory cells are localized and concentrated where?
in anatomically defined organs or tissues that constitute the lymphoid system.
Classification of Lymphoid Organs and Tissues is based on?
(1) the level to which they participate in the matu- ration of lymphocytes and
(2) provision of a suitable environment for the inter- action between foreign antigen and T and B lymphocytes.
Central [Primary] lymphoid organs regulate what?
regulate production and maturation of lymphocytes from lymphoid stem cells, ie, generate lymphocytes that are individually different to meet the threat posed to an animal by the large number of microbial pathogens, the concept being “one cell, one specificity.”
What are the Central [Primary] lymphoid organs of mammals?
Bone marrow, Thymus
What are the Central [Primary] lymphoid organs of avian?
Bursa of Fabricius, Thymus
Peripheral [Secondary] lymphoid organs provide what?
Provide the environment where ma- ture lymphocyte responses to foreign antigens are initiated and develop.
List the Peripheral [Secondary] lymphoid organs
Spleen
Lymph nodes
Mucosa-associated lymphoid tissue [MALT]
The spleen responds to what?
Responds to blood-borne antigens.
The lymph nodes respond to what?
Respond to lymph-borne antigens, ie, antigens entering the body via the skin and mucosa or from parenchymal organs and connective tissues.
Mucosa-associated lymphoid tissue [MALT] does what?
Includes all the lymphoid tissues associated with mucosae, eg, Peyer’s patches, tonsils, etc. Protects the mucosal surfaces.
What is the Major Histocompatibility Complex (MHC)?
is a complex of genes found in all mammals that encode cell- surface MHC molecules responsible for:
(1) the rapid rejection of grafts between individuals and
(2) antigen presentation to T cells.
What are Class I MHC molecules?
Expressed on the cell membranes of most nucleated cells except neurons, erythrocytes, and cells in early embryonic life.
Bind to pep- tides derived from cytosolic proteins [endogenous antigens] and present them to cytotoxic T cells.
What are Class II MHC molecules?
Expressed on the cell membranes of professional antigen presenting cells [macrophages, dendritic cells, and B cells].
Bind to pep- tides derived from endosomal antigens [exogenous antigens] and present them to helper T cells.
T lymphocytes arise from what?
arise from lymphoid stem cells in the bone marrow.
Unlike B lym- phocytes, which mature in the bone marrow, pre-T cells migrate to what to mature?
the thymus gland to mature.
During its maturation within the thymus, the T cell expresses a what?
a unique antigen-binding receptor on its membrane, called the T cell receptor.
The process of T cell maturation also involves what?
random rearrangements of a series of gene segments encoding the cell’s antigen receptor.
Each T lymphocyte expresses about how many receptors per cell?
10^5 receptors per cell, and all 10^5 receptors on a cell and its clonal progeny have identical specificity for antigen.
T cell receptors can only recognize antigen that is associated with what?
cell membrane proteins called major histocompatibility complex [MHC] molecules.
What happens when a naïve T cell encounters antigen associated with an MHC molecule on a cell?
the T cell proliferates and differentiates into memory T cells or effector cells.
What are the two subpopulations of T cells?
T helper cells [TH] and cytotoxic T [Tc] cells.
TH cells express what?
CD4 membrane glycoproteins
Tc cells express what?
CD8 membrane glycoproteins.
Activation of both the humoral and cell-mediated branches of the adaptive im- mune system requires what?
cytokines secreted by TH cells