18) Infectious diseases summary_9744_2019

Raffles Institution Infectious Diseases 2019 Prepared by: Mrs Selvamani Nair, Ms Michelle Nah, Mr Ngan Wei Yeong 1 Infectious diseases * Infection: process where a pathogen invades and multiplies in a host and causes ill health in the host * Pathogens: 1. microorganisms that cause disease (impair normal function) by invading and multiplying in the host 2. e.g. bacteria, viruses, fungi, worms and protozoa 3. can be intracellular (i.e. in cells) or extracellular (i.e. in blood, tissue fluid and lymph i.e. in the humour) 4. have antigens on their surface * Antigens: 1. many different types can be found on one pathogen 2. triggers an immune response when specific parts of the antigen called epitopes are recognised by immune cells or antibodies * Epitopes: 1. parts of a single antigen 2. each have a specific conformation complementary in shape and charge to a specific antigen-binding site of an antibody or T cell receptor or B cell receptor * Cells of the Immune System: 1. Phagocytes a) macrophages  an antigen presenting cell (APC) which resides in tissues  are produced when monocytes in the blood enter tissues and differentiate b) dendritic cells  an antigen presenting cell (APC) which resides in tissues c) neutrophils  found in blood Immune System Innate Immune System (1st line of defense) Adaptive Immune System (2nd line of defense) Cellular Components Cell-mediated Response Humoral Response 1. Skin  Acidic pH and inhibits microbial growth 2. Mucous membranes  contain antimicrobial proteins, e.g. lysozyme, which break down bacterial cell walls  release fluids e.g. saliva, tears to wash away pathogens and prevent their attachment Phagocytes 1.Macrophages 2.Dendritic cells 3.Neutrophils Antigen presenting cells (APCs) Properties of the innate (non-specific) immune response: 1. is non-specific  attacks anything that is foreign or non-self 2. is rapid  responds as soon as pathogen is encountered 3. has no memory  responds the same way to repeat encounters with the same pathogen Properties of the adaptive (specific) immune response: 1. is specific  recognises only a specific antigen on a pathogen 2. takes time to develop  this applies to first exposure to pathogen (i.e. primary immune response) 3. shows memory  responds quickly to repeat encounters to the same pathogen (i.e. secondary immune response occurs rapidly) Mediated by cytotoxic T cells that kill cells infected with intracellular pathogens Mediated by antibodies (secreted by plasma cells) which target extracellular pathogens Barriers pathogen encounter 1