Lymphoid System
Histologically this system consists of large, diverse population of leukocytes located within every
tissue of the body and lymphoid organs interconnected only by the blood and lymphatic circulation
Immunologists recognize two partially overlapping lines of defense against invaders or other
abnormal, potentially harmful cells: innate immunity and adaptive immunity
Primary lymphoid organs: thymus and bone marrow
Secondary lymphoid organs: lymph nodes, spleen, lymphoid tissue in mucosa of digestive system
(tonsils, Peyer patches, appendix).
Innate and Adaptive immunity:
o Innate: immediate, nonspecific actions, including physical barriers.
o If bacteria and other parasites penetrate the external barriers, they are quickly removed by neutrophils.
o Toll-like receptors (TLR) on leukocytes allow the recognition and binding of surface components of invaders.
o Natural killer cells (NK) destroy unhealthy host cells, including those infected with virus or bacteria, and
tumorigenic cells.
o Leukocytes and other specialized cells form antimicrobial chemicals which are part of the innate immunity:
a) Hydrochloric acid (HCl) and organic acids (kill or inhibit growth)
b) Defensins (kill bacteria by disrupting the cell walls.)
c) Lysozyme (hydrolyzes bacterial cell wall)
d) Complement (system of proteins in plasma, that react with bacterial surface components to aid removal of bacteria)
e) Interferons (kill virus-infected cells to resist viral infection)
o Adaptive Immunity is acquired gradually by exposure, more specific, slower.
I. It involves B and T lymphocytes.
II. They use APCs
III. Involve production of memory lymphocytes
Cytokines:
o Involved in both, innate and adaptive
o They are a diverse group of peptides and glycoproteins that work in a paracrine mode of action.
o Their major responses include:
I. Direct cell movement (chemotaxis) toward sites of inflammation. Such cytokines are named chemokines.
II. Increased mitotic activity in certain leukocytes, both locally and in the bone marrow.
III. Stimulation or suppression of lymphocyte activities in adaptive immunity. This cytokine are called
interleukins.
IV. Stimulated phagocytosis or directed cell killing by innate immune cells.
, o Most cytokines have multiple target cells.
Antigens are molecules that are
recognized by cells of the adaptive
immune system.
o Immune cells recognize an antigen at a small
molecular domain called the epitope.
o Immune response to them can be cellular,
humoral, or both.
An antibody is a glycoprotein of the
immunoglobulin family that interacts
specifically with an antigenic
determinant.
o They are secreted by plasma cells that arise by
terminal differentiation of clonally proliferating
B lymphocytes.
Immunoglobulin consist of 2 identical
light chains and 2 identical heavy
chains bound by disulfide bonds.
Classes of antibodies:
o IgG:
I. most abundant class (75 to 85%)
II. it is highly soluble
III. its half-life is > 30 weeks
IV. crosses placental barrier into fetal circulation
this confers passive immunity against
infections until the newborn has his own
adaptive immune system.
o IgA:
I. Present in almost all exocrine secretions as a
dimeric form
II. Produced by plasma cells in the mucosae of
digestive, respiratory, and reproductive tracts.
Histologically this system consists of large, diverse population of leukocytes located within every
tissue of the body and lymphoid organs interconnected only by the blood and lymphatic circulation
Immunologists recognize two partially overlapping lines of defense against invaders or other
abnormal, potentially harmful cells: innate immunity and adaptive immunity
Primary lymphoid organs: thymus and bone marrow
Secondary lymphoid organs: lymph nodes, spleen, lymphoid tissue in mucosa of digestive system
(tonsils, Peyer patches, appendix).
Innate and Adaptive immunity:
o Innate: immediate, nonspecific actions, including physical barriers.
o If bacteria and other parasites penetrate the external barriers, they are quickly removed by neutrophils.
o Toll-like receptors (TLR) on leukocytes allow the recognition and binding of surface components of invaders.
o Natural killer cells (NK) destroy unhealthy host cells, including those infected with virus or bacteria, and
tumorigenic cells.
o Leukocytes and other specialized cells form antimicrobial chemicals which are part of the innate immunity:
a) Hydrochloric acid (HCl) and organic acids (kill or inhibit growth)
b) Defensins (kill bacteria by disrupting the cell walls.)
c) Lysozyme (hydrolyzes bacterial cell wall)
d) Complement (system of proteins in plasma, that react with bacterial surface components to aid removal of bacteria)
e) Interferons (kill virus-infected cells to resist viral infection)
o Adaptive Immunity is acquired gradually by exposure, more specific, slower.
I. It involves B and T lymphocytes.
II. They use APCs
III. Involve production of memory lymphocytes
Cytokines:
o Involved in both, innate and adaptive
o They are a diverse group of peptides and glycoproteins that work in a paracrine mode of action.
o Their major responses include:
I. Direct cell movement (chemotaxis) toward sites of inflammation. Such cytokines are named chemokines.
II. Increased mitotic activity in certain leukocytes, both locally and in the bone marrow.
III. Stimulation or suppression of lymphocyte activities in adaptive immunity. This cytokine are called
interleukins.
IV. Stimulated phagocytosis or directed cell killing by innate immune cells.
, o Most cytokines have multiple target cells.
Antigens are molecules that are
recognized by cells of the adaptive
immune system.
o Immune cells recognize an antigen at a small
molecular domain called the epitope.
o Immune response to them can be cellular,
humoral, or both.
An antibody is a glycoprotein of the
immunoglobulin family that interacts
specifically with an antigenic
determinant.
o They are secreted by plasma cells that arise by
terminal differentiation of clonally proliferating
B lymphocytes.
Immunoglobulin consist of 2 identical
light chains and 2 identical heavy
chains bound by disulfide bonds.
Classes of antibodies:
o IgG:
I. most abundant class (75 to 85%)
II. it is highly soluble
III. its half-life is > 30 weeks
IV. crosses placental barrier into fetal circulation
this confers passive immunity against
infections until the newborn has his own
adaptive immune system.
o IgA:
I. Present in almost all exocrine secretions as a
dimeric form
II. Produced by plasma cells in the mucosae of
digestive, respiratory, and reproductive tracts.
