Download Non-specific defense mechanisms

Non-specific defense
mechanisms
• 1st line- skin and mucous
– Cilia lined trachea, hairs in pathways
• 2nd line– phagocytic WBC
– antimicrobial proteins (compliment & interferon)
– inflammatory response
Phagocytic WBC
• Neutrophils (60-70% of all WBC)
• attracted by chemical signals from damaged cells and enter
tissues
• Monocytes (5% of all WBC)
– develop into macrophages which use psudopodia to
capture invading bacteria
• Eosinophils (1.5% of all WBC)
– used to attack bigger invaders “worms”
• natural killer cells
– attack virus-infected cells to prevent spreading
Antimicrobial proteins
• Compliment – various proteins in the plasma that
work with antibodies, phagocytes, and on their
own non-specifically to enhance immune
response.
• interferon-proteins secreted by virus-infected
cells. Inhibits virus reproduction in neighboring
cells. Can be mass produced now and may be used
to treat cancer patients.
Inflammatory response
• 1. Damaged tissues release chemical signals such as
histamine (contained in basophils WBC and mast cells of
connective tissue) and prostaglandins to increase blood
flow.
• 2. Prostaglandins induce vasodilation and increased
permeability to clotting factors.
• 3. Chemokines release chemicals that mediate the arrival
of phagocytic cells to the area
• Phagocytes consume debris and pathogens forming pus
• Sometimes allergies cause massive release of histamine to
“safe” invaders, so antihistamines block this response
Specific defense (3rd line)
• Four major features
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Specificity (recognize particular antigens)
diversity (responds to millions of different invaders)
self/nonself recognitionmemory - acquired immunity so the second time
body is infected the response will be quick enough to
avoid serious infection. This is the basis for
vaccination.
Cell surface markers
• Blood cells A, B, and Rh Factor proteins
• Major histocompatibility complex (MHC) are
glycoproteins marking cell as self
• MHC class I are on all nucleated cells
• MHC class II are only on specific immune cells
• These allow cytotoxic T-cells (MHC I) and helper
T-cells (MHC II with antigen fragments attached)
to bond to cells
• Huge amount of variety, so each individual is
unique in their MHC proteins.
Humoral immunity
• Results in production of antibodies
– Free antigens activate B- cells
– B- cells make the antibodies and then develop
into Plasma cells and memory B-cells for next
time
– Plasma cells secrete antibodies
– antibodies attach to antigens making them easy
“prey” for phagocytes and complement
Formation of lymphocytes
• Lymphocytes are WBC formed in the bone
marrow. (B and T cells)
• B- cells fully develop in the bone marrow
before being released
• T - cells then travel to the the thymus for
further development before leaving.
• In the thymus they pick up recognition of
MHC complex as self.
Cell-mediated immune response
• Antigens displayed by MHC class I glycoproteins in
infected cells activate Cytotoxic T cells
• Cytotoxic T cell give rise to memory T cells and
Active cytotoxic T cells
• Activated cytotoxic T cells attack cells by binding to
and lysing them
2nd exposure
• 2nd time the antigen stimulates Memory B
cells and memory T cells to activate both
humoral and cell-mediated responses.
• 2nd defense (about 3 days) where as 1st
response is usually 7-10 days.
• Supressor T cells are thought to help turn
off the immune response when antigens are
gone.
Antibodies
• A class of proteins referred to as the immunoglobulins
(Ig) with 4 polypeptides (2 heavy chains and 2 light
chains) held together by disulfide bridges to give them
their quaternary structure
• Most of the antibody structure is identical for all
antibodies with the “tips” variable that bind to the
epitope (exposed) region on the antigen surface.
• Five types of immunoglobulins are divided by their
constant regions IgM, IgG, IgA, IgD, and IgE.
Immunoglobulin classes
• IgM: large molecule that initiates response by
agglutinating (clumping up) the antigens
• IgG: Most plentiful, triggers complement
proteins
• IgA: Prevents attachment of antigens to
epithelial linings. Plentiful in mucus.
• IgD: found on B-cells and probably initiate the
development of B-cells into plasma cells
• IgE: small number, trigger the histamine release
of basophils and mast cells via receptor binding.
Helper T-cells
• Helper T cells are stimulated by interleukin
1 of macrophages after engulfing antigens
and presenting them.
• Helper T cells in turn stimulate the B cells
of the humoral defense and the Cytotoxic T
cells of the Cell mediated defense by
releasing interleukin 2.