immune ii Flashcards
Adaptive immune system
- protects against infectious agents and abnormal body cells
- amplifies inflammatory response
- activates complement
- must be primed by initial exposure to specific foreign substance
- Specific, systemic, and has memory
humoral immunity
- antibodies, produced by lymphocytes, circulating freely in body fluids
- bind temporarily to target cells –> temporarily inactivate and mark for destruction by phagocytes or comlement
- has extracellular tergets
Cellular immunity
lymphocytes act against target cell:
- directly by killing infected cells
- indirectly by releasing chems that enhance inflammatory response or activating other lymphocytes or macrophages
- has cellular targets
Antigens
- substances that can mobilize adaptive defenses and provoke an immune response
- targets of all adaptive immune responses
- most are big, complex molecules not normally found in body (non-self)
Complete antigens
- Immunogenicity = ability to stimulate proliferation of specific lymphocytes
- reactivity = ability to react with activated lymphocytes and antibodies released by immunogenic reactions
-e.g. foreign protein, polysaccharides, lipids, and necleic acids
Haptens (incomplete antigens)
- small molecules, not immunogenic by themselves (peptides, nucleotides, some hormones)
- may be immunogenic if attached to body proteins and combination is marked foreign
- causes immune system to mount harmful attack
e.g. poison ivy, animal dander, detergents, and cosmetics
Antigenic determinants (epitopes
- only certain parts (antigenic determinants) of entire antigen are immunogenic
- antibodies and lymphocyte receptors bind to them as enzyme binds substrate
- most naturally occuring antigens have numerous epitopes that mobilize several dif lymphocytes and form dif kinds of antibodies angainst them
MHC proteins (major histocompatibility complex)
Self antigens on surface of cells
MHC antigens
-MHC or human leukocyte antigens
-normal func to help T cells recognize foreign or self
-class I MHC = built into all body cells except RBCs
-Class II MHC = only on antigen presenting cells
Three cells of adaptive immune system
- B lymphocytes (humoral immunity)
- T lymphocytes (cellular immunity)
- Antigen presenting cells (APCs) (Don’t respond to specific antigens; play essential auxiliary role in immunity)
5 general steps of lymphocyte development
- Origin - all originate in red bone marrow
- Maturation - in thymus or bone marrow
- Seeding secondary lymphoid organs and circulating
- Antigen encounter and activation
- Proliferation and differentiation
Lymphocyte maturation
- “educated” to become mature –> B cells in bone marrow, T cells in thymus
- Immunocompetence: lymphocyte can recognize one specific antigen by binding to it –> B and T cells only have one type of antigen receptor
- Self-tolerance = lymphocytes unresponsive to own antigens
B cell maturation
-mature in red bone marrow
-positively selected if successfully make antigen receptors
-those that are self-reactive are eliminated by apoptosis (clonal deletion
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Seeding secondary lymphoid organs and circulation
- immunocompetent B and T cells not yet exposed to antigen called naive
- exported from primary lymphoid organs (bone marrow and thymus) to “seed” secondary lymphoid organs (lymph nodes, spleen, etc…) –> increases chances of encountering antigen
clonal selection
- naive lymphocytes’ first encounter with antigen –> selected for further development
- If correct signals present, lymphocyte will complete its differentiation
Antigen Receptor Diversity
-genes, not antigens, determine which foreign substances immune system will recognize –> immune cell receptors result of acquired knowledge of microbes likely in environment
Lymphocytes make up to a billion types of antigen receptors –> coded for by 25ooo genes –> gene segments are shuffled by somatic recombination
Antigen presenting cells (APCs)
- engulf antigens
- present fragments of antigens to T cells for recognition
Major types
- dendritic cells in CT and epidermis
- Macrophages in CT and lymphoid organs
- B cells
Dendritic cells (APC)
- phagocytize pathogens
- enter lymphatics to present antigens to T cells in lymph node
- most effective antigen presenter
- key link bt innate and adaptive immunity
Macrophages (APC)
- widespread in lymphoid organs and CT
- present antigens to T cells to activate themselves into voracious phagocytes that secrete bactericidal chemicals
B lymphocytes (APC)
- don’t activate naive T cells
- present antigens to activated helper T cells to assist own activation
Exogenous antigens
- present in fluid outside body cells
- APCs ingest antigen, process, and place next to MHC-II molecule in plasma membrane, and present to T cells
Endogenous antigens
- antigens inside body cells
- infected cell displays antigen next to MHC-I
Antibody mediated immunity
- During activation, antigen binds to B cell receptor
- Can respond to unprocessed antigen
- Response much more intense when B cell processes antigen –> antigen taken into B cell, combined with MHC-II, moved to plasma membrane–> helper T cell binds and delivers costimulation (interleukin 2 and other cytokines)
-B cell undergoes clonal selection: plasma cells secrete antibodies –> memory B cells don’t secrete antibodies, but wait for reappearance of antigen
Immunological memory: primary immune response
- cell proliferation and differentiation upon first antigen exposure
- lag period: 3-6 days
- peak levels of plasma antibody are reached in 10 days
- antibody levels then decline
Immunological memory: secondary immune response
- re-exposure to same antigen gives faster, more prolonged, moreeffective response
- sensitized memory cells respond within hours
- antibody levels peak in 2-3 days at much higher levels
- antibodies bind with greater affinity
- antibody level can remain high for weeks to months
Active humoral immunity
-when B cells encounter antigens and produce specific antibodies against them
2 types:
- Naturally acquired = response to bacterial or viral infection
- Artificially acquired = response to vaccine or dead/attenuated pathogens
Vaccines
- mostly dead or attenuated pathogens
- spare us symptoms of primary response
- provide antigentic determinants that are immunogenic and reactive
Passive humoral immunity
- readymade antibodies introduced into body
- B cells aren’t challenged by antigens
- immunological memory doesn’t occur
- protection ends when antibodies degrade
2 types of passive humoral immunity
- Naturally acquired = antibodies delivered to fetus via placenta or to infant through milk
- Artificailly acquired = injection of serum, like gamma globulin –> immediate protection, but ends when antibodies naturally degrade in body
