Adaptive Immunity :the Immune System Flashcards
Immunity
Specific antibody and lymphocyte response to an antigen
Antigen (Ag)
A substance the body identifies as foreign and to which it produces specific antibodies or sensitized Tcells
Antibody (Ab)
Proteins made in response to an antigen
Humoral immunity
carried out by antibodies circulating in the blood.
Antibodies are produced by B lymphocytes that have matured into plasma cells
Cell mediated immunity :
carried out by T lymphocytes and occurs at the cellular level
Antigen:
a substance the body identifies as foreign and toward which it mounts an immune response
• Most are large, complex proteins
Hapten
a small molecule that can act as an antigen if it binds to a larger protein molecule (ex: penicillin)
Antibody
A protein produced in response to an antigen and is capable of binding specifically to the antigen
Antibodies are produced by
Plasma cells ( matured from B cells)
A typical antigen:
antibody reaction: gram-negative bacterial pathogen may have several antigens, or immunogens (flagella, pili and cell wall)
Antibodies recognize and react with
Antigenic determinants or epitopes
5 classes of immunoglobulins (Igs)
- IgG
- IgM
- IgA
- IgE
- IgD
IgG antibodies:
• Main class of Ab in blood (80% of serum antibodies)
• Only Ig that crosses placenta
• Monomer
IgM antibodies
• First Ab produced in response to infection
• 5-10% of serum antibodies
• Pentamer
Primary Response to an Ag:
first contact with Ag is characterized by IgM followed by IgG
Secondary response to an Ag (memory):
2nd exposure to same Ag, the response is rapid & results in high Ab titer (mostly IgG)
IgA antibodies
• In secretions (tears, colostrum, saliva, mucus)
• 10-15% of serum
antibodies
• Dimer
IgE antibodies
• Allergic reactions; lysis of parasitic worms
• On mast cells and basophils
• 0.002% of serum antibodies
• Monomer
IgD antibodies
• On B cells, initiate immune response
• Monomer
• 0.2% of seum Abs
Specific immune responses are carried out by
lymphocytes which develop from stem cells
(as do other WBCs, RBCs, and platelets)
• B lymphocytes (B cells)
• T lymphocytes ( T cells)
Differentiation of T AND B cells
Clonal selection:
B cells become activated when an Ag reacts with:
Specific receptors on its surface
Clonal selection:
The activated B cell produces:
A clone of plasma cells and memory cells
Humoral immunity:
Plasma cells…
Synthesize and release antibodies
Humoral immunity
Memory cells remain in:
Lymphoid tissue ready to respond to subsequent exposure to the same antigen
Humoral immunity : self-tolerance
Body doesn’t make
Ab against itself
Clonal deletion:
-the process of destroying B and T cells that react to self antigens
this process takes place in the bone marrow and thymus. Removes those lymphocytes that have receptors for self antigens
B cell receptor (BCR)
Antibody that remains associated with the
cytoplasmic membrane of the B lymphocyte
BCR
• Each B lymphocyte has multiple copies of a single type of BCR
• Antigen binding site is identical to that of the secreted antibody for that particular cell
• Each BCR is complementary to only one antigenic determinant
• The BCRs on all of an individual’s B cells are capable of recognizing millions of different antigenic determinants (EACH INDIVIDUAL B CELL RECEPTOR)
T cell-independent Antigens
stimulate B cells directly
– Larger, repeating
– exogenous
T-dependent Ags require help of
antigen presenting cells (APCs) and T helper cells to stimulate B cells (phagocytized by a phagocyte
– Smaller not as numerous
– endogenous
Antigen-Presenting Cells
• Digest antigen
• Ag fragments on APC surface with MHC – B cells
– Dendritic cells
– Activated macrophages
Interleukin -1
Stimulates TH cells
Interleukin-2
Activates TH, B, TC, and NK cells
Interleukin- 12
Differentiation of CD4 cells
Y-interferon
(Gamma)
Stimulate macrophage activity
Chemokines
Induce migration of leukocytes to infection
MHC (very important in transplants/grafting)
Major Histocompatibility complex
in all cells. Accepts or rejects ag as compatible or not. Attaches to non compatible ag and presents it to T cell
Activation of B cells w helper T cells
Cell mediated immunity
• Involves the direct actions of T cells
• T cells respond to intracellular (endogenous) Ags, viruses, tumors and reject transplanted tissue
• Some activated T cells become memory cells
What are the 3 T cells?
• T Helper Cells (TH) = CD4 cells
• T Cytotoxic Cells (TC) = CD8 cells
• T Regulatory Cells (Treg)
• T Helper Cells (TH) = CD4 cells
present T dependent Ags to B cells, stimulate other T & B cells
• T Cytotoxic Cells (TC) = CD8 cells
differentiate into cytotoxic T Lymphocytes (CTL) which destroy target cells with perforin
differentiate into cytotoxic T Lymphocytes (CTL) which destroy target cells with perforin
• T Regulatory Cells (Treg)
suppress T cells against self
subset of CD4 TH cells
formerly called T suppressor cells
Humoral vs cellular immune system
T cytotoxic cells
Primary and Secondary Responses
In humoral immunity the primary response to an antigen occurs when the antigen is first recognized by host B cells
Primary response of B cells can occur by two mechanisms
B cells can be activated by binding antigen, proliferating and forming plasma cells (T-independent antigens)
Produces IgM antibody and no B memory cells are formed (T-dependent antigens)
Secondary response:
when an antigen recognized by memory cells enters the blood
The central role of helper T cells
Cell-Mediated Immunity
-Involves the direct actions of T cells(makes memory cells and clones themselves
• T cells interact directly with other cells that display foreign antigens
• Involves the differentiation and actions of different types of t cells Th2, Tc and Tm
• Involves production of chemical mediators (cytokines)
– Cytokines: lymphokines and interleukins
Cell-Mediated Immune Reaction
• Involves the response of T lymphocytes
• T cells cannot be activated directly by antigens
• Macrophages that have processed an antigen secrete the lymphokine interleukin-1 (IL-1), which activates T helper cells
• T helper cells secrete interleukin-2 (IL-2) and activate delayed hypersensitivity cells and cytotoxic killer cells
• IL-1 and IL-2 cause undifferentiated cells to become natural killer cells
Natural Killer (NK) Cells
Granular leukocytes destroy cells that don’t express MHC I
• Kill virus-infected and tumor cells • Attack parasites
AIDS destroys TH cells, thereby impairing both humoral and cell-mediated immunity…
Will be affected
Cell Mediated Immunity (*know)
