Comparative immunology Flashcards
(14 cards)
Roles of the primary lymphoid tissues and examples
Where lymphocytes are generated, matured and differentiated
Bone marrow
Thymus
Bursa of Fabicus in birds)
Ileal Peyer’s patch in sheep, cattle, pigs, dogs and horse
Appendix
Caeceal patch in rabbits
Secondary lymphoid tissues
Where lymphocytes interact with antigen presenting cells
Lymph nodes
Mucosal-associated lymphoid tissue
Spleen
Structure of the thymus
Small thoracic organ near the heart
Lymphocytes produced by the bone marrow are transported there in the blood
T lymphocyte maturation and selection occurs here
T cells arrive mature and leave immature
Active when young then shrinks and atrophies when older, producing fewer T cells
Cortex
Densely populated with lymphocytes (immature T cells)
Occasional macrophages which remove immature T cells which have undergone apoptosis
Immature to adult T lymphocyte in the cortex then migrate to the medulla
Medulla
Presents antigens to lymphocytes
Thymic selection where the majority die as they don’t recognise self (~95%) and survivors become functional T cells
Survivors enter circulation and move through secondary lymphoid tissues
Lymph nodes
Arises late in foetal life and persists in adults
Fluid and antigens drain from tissues into afferent lymphatics
Antigen is encountered
Lymphocytes are activated and proliferate
Encapsulated organ
Lymphocytes recirculate into the blood via efferent lymphatics and thoracic duct
Organ enlarges under immune response
Naïve lymphocytes enter lymph nodes through high endothelial venules
What is lymph fluid?
Filters out of capillaries and drains into lymphatic vessels to become lymph
Eventually drains into venous blood after passing through secondary lymphoid organs
Lymph drains interstitial fluid, transports dietary lipids and facilitates immune response by draining antigens from tissues to lymph nodes and eventually to the blood
Where do mucosal associated lymphoid tissues (MALT) operate
Found in the GI tract, respiratory tract, genitourinary tract, appendix, tonsils, Peyer’s patches
Very dense areas of lymphocytes
Especially around bronchial lumens and lamina propria and sub-mucosa of large and small intestines
Peyer’s patches
In ileal submucosa of small bowel
Germinal centres prominent as sites of antibody production
Detects antigens that diffuse across the intestinal epithelia via microfold cells
What is colostrum
Produced in mammary glands in the last few weeks of pregnancy
Active transfer of Igs from blood to mammary glands under influence of oestrogen and progesterone
Main colostrum antibody is IgG
As colostrum changes to milk Ig content reduced and theres proportionally more IgA
Igs derived from serum
Transfer of colostrum
Ingested and passes into the GI tract where enzyme levels are low or blocked so proteins can reach the small intestine
Newborns have a specialised Fc receptor on intestinal epithelia (for 24 hours)
Intestine is only permeable for a short period, begins to decline after 6 hours
Distinguish between primary and secondary immunodeficiency
Primary is genetic or congenital, may also be hereditary
Secondary - occurs due to secondary factors (drugs or infection)
Equine SCID (severe combined immunodeficiency)
Defect in DNA dependent protein kinase
Prevents DNA repair resulting in a failure to form functional antigen binding regions in their TCR and BCR
No functional T or B lymphocytes in circulation or tissues
Foal sicken after maternally derived antibodies have left circulation
Autosomal recessive
Overwhelming infections, death within 4-6 months
Canine SCID
Female carriers, X-linked so only a problem in males
Thymus has a low number of lymphocytes
Low T cell numbers in circulation, no IgA or IgG but normal IgM so presumed lack of Th cells
