Veterinary Immunology PDF

Veterinary Immunology By Dr. Betelihem Tegegne  The basics of Immunology Brief history of immunology The discipline of immunology grew out of the observation that individuals who had recovered from certain infectious diseases were thereafter protected from the disease. The...

Veterinary Immunology By Dr. Betelihem Tegegne  The basics of Immunology Brief history of immunology The discipline of immunology grew out of the observation that individuals who had recovered from certain infectious diseases were thereafter protected from the disease. The Latin term immunis, meaning “exempt” is the source of the English word immunity, meaning the state of protection from infectious disease. The scientific study of the immunity/ body defense is immunology.  Early vaccination led the way to immunology 12th century, the Chinese had observed that persons who recovered from smallpox were resistant to further attacks of this disease. So, they deliberately infected infants with smallpox by inserting scabs from infected individuals into small cuts in their skin, and infants were protected from smallpox (Variolation) Early 18th Century: Variolation spread across Europe In 1718, Lady Mary Montagu spread variolation to England.  Con’t.. The method was significantly improved by the English physician Edward Jenner, in 1798. 19th Century: Rinderpest outbreak (Killed huge numbers of cattle). Since none of the traditional remedies appeared to work and the skin lesions in affected animals vaguely resembled those seen in smallpox, it was suggested in 1754 that inoculation might help.  Con’t.. Variolation: Soak a piece of string in the nasal discharge from an animal with rinderpest and then inserting the string into an incision in the dewlap of the animal. It induced milder infection than natural infection and animals were protected from RP. RP was eradicated in June 2011 via Vaccination  Scientists behind the science of Immunology Name Timeline Major Impact and country Edwar 1798, Observation: Milkmaid (mild disease of Cowpox) were protected d English from smallpox Jenner physician Developed an Idea: to introduce fluid from a cowpox pustule into people Test idea: fluid injected 8 years old boy and infected with smallpox, were protected from the diseases. Vaccination is safer than Variolation Louis 1879, Old P Multocida culture protected chicken from cholera (live Pasteu French attenuated vaccine), attenuated strain as a vaccine r Microbiolo gist Vaccine: latine word vacca meaning « cow, » in honour of Jenner’s work. 1881 Anthrax Vaccine: heat treated live attenuated B anthracis as a vaccine, protecetd the vaccinated sheep from anthrax. 1882 Developed Rabies vaccine from Rabbit (Live attenuated)  Immunity (immune response) The defenses of the body, collectively called the immune system, consist of complex, interacting networks of biochemical and cellular reactions. Immunity refers to the state of protection from infectious diseases. Con’t..  Con’t.. Immunology is the science that studies the mechanisms that allow living beings to survive against the continuous attack of microorganisms in the environment. Immunogens: Substances that induce an immune response Antigens: Molecules that are recognized during the immune response  Con’t.. Multiple mechanisms are needed to ensure freedom from invasion. These include physical barriers that exclude invaders, innate immunity that provides rapid initial protection, and adaptive immunity that provides prolonged effective immunity.  Innate response Adaptive response Barriers (immediate) (early) (later) Cells, tissues and organs of the immune system Immune cells Composition of blood  Leucocytes (white blood cells)  Classified into two major groups depending on the presence or absence of specific cytoplasmic granules. 1. Granulocytes (Granular leucocytes)  Have specific granules, nuclei of mature or nearly mature granulocytes are composed of several segments.  The nuclei may have two, three or four segments.  Include neutrophils, eosinophils, and basophils. 14  Con’t.. 2. Agranulocytes (Nongranular leucocytes)  Do not have specific granules and possess a spherical, oval or horseshoe-shaped nucleus.  Lymphocytes and monocytes 15  Granulocytes Neutrophils The first cells attracted to sites of inflammation are neutrophils. Neutrophils bind, phagocytose, and kill invading microorganisms. Ingested microorganisms are killed by potent oxidants through a process called the respiratory burst, by antibacterial proteins called defensins and by lytic enzymes.  Eosinophils  The cytoplasm is full of granules which stain bright orange /red with eosin stain.  Granules are larger and more spherical.  Bilobed nucleus.  These cells are phagocytic and have a special avidity for antigen-antibody complexes.  Increase in the numbers during allergic reactions or parasitic infections.  Basophils  Only a small percentage (less than 1% ) of total leukocytes.  Their nucleus is bi-lobed  Large, round to oval, blue granules 18  Agranular leukocytes  Monocytes  Are the largest of the leukocytes (15 to 20 µ in diameter).  Have eccentric nucleus of highly variable shape (oval, irregular, kidney-shaped, or horseshoe- shaped).  Migrate from the bloodstream to other tissues. 19  Con’t.. Lymphocytes  Their nucleus is very large and thin layer of cytoplasm.  These cells play an important role in the immune response. T-lymphocytes act against virus infected cells and tumor cells. B-lymphocytes produce antibodies. 20  Lymphoid Organs A number of morphologically and functionally diverse organs and tissues have various functions in the development of immune responses. These can be distinguished by function as the primary and secondary lymphoid organs.  Con’t.. Primary Lymphoid Organs The organs that regulate the developme nt of lymphocytes are called primary l ymphoid organs. The primary lymphoid organs develop early in fetal life.  Con’t.. As animals develop, newly produced, immature lymphocytes migrate from the bone marrow to the primary lymphoid organs, where they mature. The primary lymphoid organs are not sit es where lymphocytes encounter foreign antigens, and they do not enlarge in response to antigenic stimulation.  Con’t.. Thymus The thymus is located in the thoracic cavity in front of and below the heart. In horses, cattle, sheep, pigs, and chicken, it also extends up the neck as far as the thyroid gland. The size of the thymus varies, its relative size being greatest in the ne wborn animal.  Con’t.. The thymus is the site of T-cell development and maturation. -Cortex: Site of immature thymocytes (come from Bone Marrow) -Medulla: Site of mature thymocytes in their way out  Con’t.. The function of the thymus is to generate and select a repertoire of T cells that will protect the body from infection. As thymocytes develop, an enormous diversity of T-cell receptors is generated by a random process that produces some T cells with receptors capable of recognizing antigen-MHC complexes.  Con’t.. Bone marrow In humans and other animals, bone marrow is the site of B-cell origin and development.  Con’t.. Like thymic selection during Tcell maturation, a selection process within the bone marrow eliminates B cells with self-reactive antibody receptors. Bone marrow is not the site of B-cell development in all species. For instance birds have bursa of fabricius.  Con’t.. Bursa of Fabricius The bursa of Fabricius is found only in birds. It is a round sac located just above the cloaca.  Secondary lymphoid organs Mature lymphocytes leave the primary lymphoid organs to reside in secondary lymphoid organs, where their role is to encounter and respond to foreign antigens. In contrast to the primary lymphoid organs, the secondary lymphoid organs arise late in fetal life and persist in adults. Unlike primary lymphoid organs, they enlarge in response to antigenic stimulation.  Con’t.. Lymph Nodes Lymph nodes are round or bean- shaped filters strategically placed on lymp hatic vessels in such a way that they can sample antigens carried in the lymph.  Con’t.. Lymph nodes consist of a capsule be neath which is a reticular network fille d with lymphocytes, macrophages, and dendritic cells. The lymph node thus acts as a filter for lymph fluid. Lymph nodes… Three tissue layers – Outer cortex: APC, B cell – Paracortex: APC, T cell – Medulla: cells exit, Plasma cells APC: antigen Presenting cells (Dendritic cell, Macrophages, B cells)  Con’t.. Spleen The spleen plays a major role in mounting immune responses to antigens in the blood stream. It is a large, ovoid secondary lymphoid organ situated high in the left abdominal cavity. While lymph nodes are specialized for trapping antigen from local tissues, the spleen specializes in filtering blood and trapping blood-borne antigens; thus, it can respond to systemic infections.  Con’t.. Unlike the lymph nodes, the spleen is not supplied by lymphatic vessels. Instead, blood borne antigens and lymphocytes are carried into the spleen through the splenic artery. Thank you!!!