Third line of defense
Recognition and neutralization of foreign substances
Specific immune response: cell mediated & humoral
Cellular Components of Adaptive Immunity
** All cells have a common origin in pluripotent hematopoitic stem cells (originate in bone
1. Lymphoid Progenitor Cells
T Lymphocytes: Cytotoxic and helper
B Lymphocytes: Differentiate into plasma cells and antibody production
Natural Killer Cells: kill cells they come into contact with. Non specific
2. Myeloid Progenitor Cells
- Produce granulocytes and monocytes which phagocytise cells (BEN- basophils (allergic rx),
eosinophils (parasites) and Neutrophils (first responder)),
- Monocytes differentiate into macrophages, which will display antigen markers to be
recognized by B/T cells
-Dendritic cells are critical for processing/display of antigens to T cells. (Langerhans)
Immune Defense Concept Map Microbiology Recap of Immunity:
Adaptive: is the body’s ability to recognize and then mount a defense against distinct invaders and their
Humoral immunity: activated B cells, which secrete antibodies against pathogens. Can also
have T-independent humoral immunity, which do not rely on Th cells, which are rare. T
dependent is most common and uses Th cells (CD4’s) to activate B cells.
Cell mediated immunity: T cells only
Cytotoxic T cells: (Tc or CD8 cells), distinguished by copies of its own unique TCR as well as the
presence of CD8 cell surface glycoprotein. These lymphocytes directly kill other cells.
Helper T cells (Th or CD4 cells), presence of CD4 glycoproteins.
-assist in regulating the activity of B cells and cytotoxic T cells during immune responses by providing
signals and grown factors (cytokines).
1. Type 1: assist cytotoxic T cells and innate macrophages
2. Type 2: function in conjunction with B cells
Major histocompatibility complex proteins (MHC proteins) and processing antigens make it so T
lymphocytes can recognize epitopes.
MHC antigens are glycoproteins found in the membranes of most cells in animals
MHC proteins in the CM function to hold and position epitopes for presentation to T cells.
-Class I MHC molecules: are found on the CM of all nucleated cells.
-Class II MHC molecules:
- Antigen-presenting cells (APC’s), are B cells, macrophages and dendritic cells
which are regularly present antigens.
-The major function is secretion of soluble antibodies, which is part of the humoral immunity (against a
-Specificity comes from membrane proteins called B Cell Receptors (an immunoglobulin)
-Immunoglobulin’s have the light chains/heavy chains/ variable region (antigen- binding site).
-All the BCR’s of a particular cell are the same because the variable regions are identical.
- When an antigenic epitope stimulates a specific B cell via the B cell’s unique BCR:
- the B cell responds by undergoing cell division, giving rise to offspring that
secrete immunoglobulin’s into the blood/lymph.
- The immunoglobulins act against the epitope shape that stimulated the B cell.
These activated immunoglobulin-secreting B lymphocytes are called plasma
cells, which have RER/golgi.
Memory B cells: B lymphocytes that migrate to lymphoid tissues to await a subsequent encounter with
antigen previously encountered.
-In contrast to plasma cells, these cells retain their BCR’s and persist in lymph for years, ready to initiate
an antibody production if the same epitope is encountered again. Lymphatics
Important in establishing the immune response
Central organs: bone marrow and thymus
Peripheral organs: spleen, lymph nodes and lymphoid tissue
Innate Immunity: non specific, involves inflammatory processes
Adaptive immunity: targeted to a specific antigen, involves T and B lymphocytes
Adaptive Immunity (cell mediated + humoral)
1. Cell Mediated Immunity
Cytotoxic T lymphocytes: CD8
Helper T lymphocytes: CD4 (TH1, TH2)
2. Humoral Immunity
Antibody secretion from plasma cells IgA, IgD, IgE, IgG, IgM
Major histocompatibility complex (MHC)
-MHC class 1 molecules recognize CD8 cytotoxic T lymphocytes
-MHC class 2 molecules recognize CD4 TH1 or TH2 helper T lymphocytes
Produced by human leukocyte antigen (HLA) genes
Primary response-Activation of the adaptive immune response with first recognition of a
Secondary response -Reactivation of the adaptive immune response with later recognition of the
-attenuated to reduce the ability to cause disease/ or killed organisms Alteration in Adaptive Immunity
1. Host defense failure: Impaired ability to mount a defense
1. Antigenic variation- many pathogens have multiple variations of antigens, making
recognition by T/B cells difficult
2. Viral latency- period of inactivity (HIV)
3. Immunodeficiency- Primary = genetic, Secondary = response to another disease
2. Hypersensitivity- inappropriate excessive immune response
Category Etiology Activated immune cells Injury
Type 1 (immediate) IgE mediated T2 helper cells, mast - allergic reaction: local,
hypersensitivity reaction cells, basophils inflammation (atopic),
systemic- life threatening
- Antigen IgE binding
induces release of chemical
mediators from mast cells
Type II antibody-mediated IgG/IgM Macrophage Reaction against normal