The intestine immune system has the challenge of reacting to pathogens while staying, comparatively unresponsive to nutrient antigens and the commensal microflora. Intestinal epithelial tissue ( 400 M2 ) is the site of most antibody production in the organic structure and the largest aggregation of T cells. Mucosal immune responses involve the gut-associated lymphoid tissue ( GALT ) . Lymphocytes are fond at three sites within the mucous membrane. They exist in organized lymphoid sums ( Peyer ‘s spots ) beneath the epithelial tissue of the terminal little bowel. Lymphocytes can besides be found within the epithelial cell bed ( intraepithelial lymph cells ) . Finally lymphocytes exist scattered, with other immunocompetent cells, within the lamina propria ( fig. 1 )
Oganisation and strusture of gut-associated lymphoid tissue ( GALT ) .
GALT is divided into two functional compartments: Peyer ‘s spots, where interaction occurs between luminal antigen and the immune system, and the diffusely distributed intraepithelial and lamina propria lymph cells.
Peyer ‘s spots have the anatomic visual aspect of secondary lymphoid variety meats. Peyer ‘s spots are covered by specialized epithelial tissue ( follicle-associated epithelial tissue ) . Some of these epithelial cells have surfaces which are wrinkled or folded. These microfold are M cells and their function is to try and actively transport particulate antigens from the lms into the ‘dome ‘ country, where priming of both T and B lymphocytes occurs. Within Peyer ‘s spots are specialized T cells that induce immature IgM- bearing B lymphocytes to exchange isotype to IgA. Primed B lympoblasts, committed chiefly to bring forthing IgA category antibody, migrate from Peyer ‘s spots, via the lymphatics and mesenteric lymph nodes, to the thoracic canal and hence into the circulation. These cells return preferentially to the lamina propria a procedure called ‘homing ‘ . Once back in the intestine, they mature into IgA plasma cells and are responsible for local and secretory immune defense mechanisms. The figure of IgA- bring forthing cells in the lamina propria far exceeds the Numberss bring forthing IgM, IgG, or IgE. The IgA surfacing the epithelial tissue is specially adapted for its map. IgA plasma cells produce monomeric IgA, which is converted into a dimer by a smaller ‘joining ‘ peptide ( J concatenation ) , besides produced y the plasma cells. Secretory constituent is a 70-KDa fragment of the polymeric Ig receptor that is synthesized by epithelial cells and is indispensable for conveyance of secretory IgA into the lms of the intestine. The polymeric Ig receptor occurs. As a consequence, the IGA dimer is released into the intestine attached to the proteolytic fragments of the receptor, now called secretory constituent stabilises the secretory IgA molecule and protects it from proteolytic onslaught enzymes in the intestine. Secretory IGA neutralises viruses, bacteriums and toxins, prevents the attachment of infective micro-organisms to gut epithelial tissue and so barricade the consumption of antigen into the systemic immune system, a function termed ‘immune exclusion ‘ .
Effector site lymph cells can be subclassified into lamina propria lymph cells ( LPLs ) and intraepithelial lymph cells ( IELs ) . LPLs have a alone phenotype-these cells are terminally differentiated effecter T cells that have tracts of stimulation that are different from peripheral blood T cells.
Additional to LPLs, big figure of natural slayer cells, mast cells, macrophages and plasma cells can besides be found in Lamina propria. T and B lymphocytes both exist in Lamina propria, but T cells predominate in a ratio of approximately four to one. These T cells do non proliferate good after stimulation of the T-cell receptor, yet produce big sums of the cytokines interleukin 2 ( IL-2 ) , IL-4, interferon-? ( IFN-? ) and tumour mortification factor-? ( TNF? ) . The IELs besides constritute a alone population of lymph cells in the organic structure, More than 80 % of IELs are CD8+ . Some IELs are cytotoxic and some have natural slayer cell activity, fuctions of import in the control of enterovirus infection. IELs besides seem to hold a function in commanding epithelial cell barrier map.
2. a ) Discuss infected ( endotoxin ) daze and toxic daze, bespeaking their similarities and differences
B ) Discuss the phagocytosis of bacterial cells and their violent death.
Phagocytosis ( cell eating ) is the chief mechanism of killing extracellular bacteriums.
It consists of four phases: attractive force ( chemotaxis ) , attachment, engulfment and killing.
Phagocytosis begins when scavenger cells move to the site where they are needed. This directed migration is called chemotaxis, and is the consequence of chemical attractive forces is known as chemotaxis agents. Chemotactic agents produced by assorted cells of the human organic structure referred as chemokines. Chimotactic agents are produced during the complement cascade and redness. When phagocytes ‘sense ‘ the presence of chemotactic agents, they move along a concentration gradient. This means they move from countries of low concentrations of chemotactic agents to the country of low concentrations. The country of highest concentration is the site where the chemotactic agents are being produced or released. For illustration the site of redness. Therefore, the scavenger cells are attracted to where they are needed. Different types of chemotactic agents pull different types of leucocytes. Some attract monocytes, other neutrophils, and still other eosinophils.
The following measure in phagocytosis is attachment of the scavenger cell to bacterial cell to be ingested. Phagocytes can merely ‘eat ‘ objects to which they can attach. ( Opsonisation is the procedure by which phagocytosis is helped by the deposition of opsonins such as antibodies or certain complement fragments onto the surface of bacterial. ) Opsonization is sometimes necessary to enable scavenger cells to attach to encapsulated bacteriums. Than the bacteriums becomes coated with opsonins. Because the scavenger cell possesses surface molecules ( receptors ) for complement fragments and antibodies, the scavenger cell can now attach to the bacterial.
The undermentioned measure is engulfment or ( consumption ) . The scavenger cell so surrounds the bacterial with pseudopodia, which fuse together, and the bacterial is ingested. Phagocytosis is a type endocytosis ( a general term outside the cell ) . Within the cytol of the scavenger cell, the bacterial is contined within a membrane-bound cyst called phagsome.
The phagosome following fuses with a nearby lysosome to organize a digestive vascular ( phagolysosome ) , within which killing and digestion occur. Lysosomes are membrane bound cysts incorporating digestive enzymes. Digestive enzymes found within lysosomes indude enzyme myeloperoxidase. Following lysosome merger, myeloperoxidase is release, which, in the nowadays of H peroxide and chloride ion, produces a potent microbicidal agent called hypochorous acid.
The killing tracts of phagocytic cells can be oxygen dependent and oxygen independent. One oxygen-dependent tract involves the decrease of O to suproxide anion. This is molecular O to which a individual odd negatron has been added ) . This so interacts with legion other molecules to give rise to a series of free groups and other toxic derived functions, which can kill bacteriums and Fungis. In neutrophils the oxidative explosion may besides move indirectly, by advancing the flux of K+ ions into the phagosome and triping microbicidal peptidases.
A 2nd O dependent tract involves the creative activity of azotic oxide from the guanidine N of L-arginine. This in bend leads to farther toxic substances such as the peroxynitrites, which result from interaction of azotic oxide with the merchandises of the O decrease tract.
Oxygen-independent killing mechanisms may be more of import than antecedently thought. Many being can be killed by cells from patients with myeloperoxidase acids. Some of this killed anaerobically, so other mechanisms must be.