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Unit 4 Immunology and Public Health Unit 4 – Immunology and Public Health 1. The Immune System a)Non-specific defences b)Specific cellular defences 2. Infectious Diseases and immunity a)Transmission and control b)Active Immunisation and Vaccination and the evasion of immune responses 2. Infectious Diseases & immunity b) Active immunisation, vaccination and evasion By the end of this section you will be able to ….. • describe the process of antigenic variation • give examples of pathogens that use antigenic variation • describe why antigenic variation poses a problem to public health • Describe how to set up an experiment to view the antibody-antigen interaction (PS) Evasion of specific immune responses • Not all diseases can be eradicated by vaccines. • Some pathogens have evolved mechanisms that evade the immune system and therefore vaccines are of no or limited use. • Pathogens can either: 1. Undergo antigenic variation • Malaria, Influenza, Trypanosomiasis (sleeping sickness) 2. Directly attack the immune system • HIV and TB Re-cap • What is antigen? • Describe the specific immune response • Describe the role of memory cells Let’s play Chinese Whispers! Malaria To prevent the red blood cells, which the malaria protozoa hide in, from being destroyed they present a protein on the cell’s surface which causes it to stick to a blood vessel wall. It is also able to switch between many genes for this protein preventing the immune system producing appropriate antibodies in time. Evolution of the FLU virus • In this diagram, the antigens can change in two ways, but importantly, it means that the antibodies produced by memory cells cannot bind to them and inactivate the pathogen. Trypanosomiasis • A protozoa called Trypanosoma brucei causes the fatal disease called trypanosomiasis or ‘sleepingsickness’. • It has a glycoprotein coat which can contain one of many different antigens. About 1% of them can vary the antigen and replace the whole ‘coat’ when the immune system attacks. • The new coat has different antigens so the immune system has to start again, giving it time to reproduce before destroying another 99%. Survive and change Survive and change Videos • Malaria: http://www.youtube.com/watch?v=qvlTOhC mxvY • Trypanosomiasis: • http://www.youtube.com/watch?v=4aVUrG O97Zg&list=PLXfKWnjanUc3He0aOwo7Uw 0MuG0jlQjci • Influenza: • http://www.youtube.com/watch?v=ugM1nIhfIA 1. Antigenic variation • Some pathogens can change their antigens, avoiding the effect of immunological memory. • Antigenic variation occurs in diseases like malaria and trypanosomiasis, and is one of the reasons why they are still so common in many parts of the world. • Antigenic variation also occurs in the influenza virus, explaining why it remains a major public health problem and why atrisk individuals require to be vaccinated every year. Antibody and Antigen interaction – using agar gel (Experiment) • Agar gel can be used to observe antibodies reacting with antigens. • The agar allows the proteins to diffuse towards each other • When they meet they bind together. This is indicated by a white line in the agar. Antibody and Antigen interaction – using agar gel (Experiment) Antigen X placed in centre well Blood plasma of Pupil A Blood plasma of Pupil B AIM: To observe the presence of antibodies against antigen X in various pupils RESULTS Blood plasma of Pupil F Blood plasma of Pupil E Blood plasma of Pupil D Blood plasma of Pupil C • What conclusion can be drawn from these results? • Pupil C wanted to investigate what other antibodies she had. Explain how she could do this. Antigen X placed in centre well Blood plasma of Pupil A Blood plasma of Pupil B Blood plasma of Pupil F Blood plasma of Pupil E Blood plasma of Pupil D Blood plasma of Pupil C More Questions! • Antigen X is actually from an Influenza virus • All the pupils have suffered from influenza. 1. Explain why a line did not form between ALL the pupils and antigen X. 2. Explain why a line DID form between 3 of the pupils and antigen X. Antigen H placed in centre well Blood plasma of Pupil A Blood plasma of Pupil B Blood plasma of Pupil F Blood plasma of Pupil E Blood plasma of Pupil D Blood plasma of Pupil C More Questions! • Antigen X was replaced with an antigen from a different virus (antigen H). • Only Pupils A and E have been vaccinated against this virus. 1. Predict the results that would be observed from this experiment. Can you now …. • describe the process of antigenic variation • give examples of pathogens that use antigenic variation • describe why antigenic variation poses a problem to public health • Describe how to set up an experiment to view the antibody-antigen interaction (PS)