Revision Part 2

Antigenic variation refers to the ability of pathogenic bacteria to alter the surface antigens they express, typically in What is antigenic variation, particularly response to selective pressures from the in the context of pathogenic bacteria? host immune system. This allows the bacteria to evade recognition and clearance by the immune system, leading to prolonged or repeated infections. Point mutations: Spontaneous mutations in the genes encoding surface antigens can lead to changes in antigenic properties. What are some mechanisms by which bacteria achieve antigenic variation? Phase variation: This mechanism involves the reversible switching of expression states of specific genes, including those encoding surface antigens. By switching between different expression states, bacteria can alter their surface antigen profile. Antigenic variation allows pathogenic bacteria to evade recognition and clearance by the host immune system. By constantly changing their surface antiWhy is antigenic variation important for gens, bacteria can avoid detection by the survival and persistence of pathoantibodies and immune cells that target genic bacteria within host organisms? specific antigens. This enables the bacteria to establish persistent or chronic infections, leading to prolonged colonization and disease. Can you name a pathogenic bacterium that is known for its extensive antigenic Neisseria gonorrhoeae (to some extent) variation? Prolonged or Chronic Infections: Antigenic variation allows pathogens to evade host immune responses, leading to prolonged or chronic infections. This 1/4 What are some potential consequences can result in persistent inflammation, tisof antigenic variation for host health and sue damage, and long-term health comimmune responses? plications for the host. The innate immune system includes various types of cells such as macrophages, neutrophils, dendritic cells, natural killer (NK) cells, and others. These cells provide the initial defense against pathogens through mechanisms like phagocytosis, inflammation, and the release of antimicrobial proteins. What are the two main branches of the adaptive immune system, and what The adaptive immune system involves T types of immune cells are involved in cells and B cells. T cells include various each branch? subsets such as helper T cells, cytotoxic T cells, and regulatory T cells, which play roles in coordinating immune responses, killing infected cells, and maintaining immune tolerance. B cells are responsible for producing antibodies, which can specifically recognize and neutralize pathogens. When cytotoxic T cells recognize infected cells displaying antigens derived from intracellular pathogens (such as virusWhat is the primary function of cytotoxic es or intracellular bacteria), they release T cells (CD8+ T cells) in the adaptive cytotoxic molecules such as perforin immune response to infection? and granzymes. These molecules induce apoptosis (programmed cell death) in the infected cells, effectively eliminating the source of infection. What is the primary function of helper T cells (CD4+ T cells) in the adaptive immune response to infection? The primary function of helper T cells is to coordinate and regulate immune responses. They do this by secreting cytokines that influence the activity of other immune cells, including B cells, cytotoxic T cells, macrophages, and others. Helper T cells help orchestrate both the 2/4 humoral immune response (involving B cells and antibodies) and the cell-mediated immune response (involving cytotoxic T cells). The primary function of B cells in the adaptive immune response to infection is to produce antibodies. When B cells encounter antigens specific to the pathogen, they undergo What is the primary function of B cells in activation, proliferation, and differentiathe adaptive immune response to infec- tion into plasma cells. Plasma cells are tion? specialized B cells that secrete large quantities of antibodies, also known as immunoglobulins. These antibodies can recognize and bind to specific antigens on the surface of pathogens, marking them for destruction by other immune cells or neutralizing their activity directly. Their primary function is to capture, process, and present antigens to T cells, What is the primary function of dendritic thereby initiating and shaping adaptive cells in the immune system's response immune responses. Dendritic cells are to infection? adept at sensing pathogens and capturing antigens from the site of infection or inflammation. Natural killer (NK) cells are a type of cytotoxic lymphocyte that plays a critical role in the innate immune response to infection. Their primary function is to What is the role of natural killer (NK) cells recognize and kill infected cells, particin the immune response to infection? ularly those that have been transformed or stressed, without prior sensitization or activation. can induce apoptosis 3/4 Type 1 hypersensitivity: Also known as immediate hypersensitivity, this reaction involves the rapid release of histamine and other mediators from mast cells and basophils upon exposure to an allergen. It is characterized by symptoms such as hives, itching, swelling, and in severe cases, anaphylaxis. Type 2 hypersensitivity: This reaction involves the binding of immunoglobulins (IgG or IgM) to antigens on the surface of host cells, leading to cell destruction through mechanisms such as complement activation, antibody-dependent cellular cytotoxicity (ADCC), or phagocytosis. Examples include autoimmune heWhat are the four types of hypersensi- molytic anemia and hemolytic disease of tivity reactions, and what distinguishes the newborn. each type from the others? Type 3 hypersensitivity: This reaction occurs when soluble immune complexes (consisting of antigens and antibodies) deposit in tissues and trigger inflammation and tissue damage. It is associated with conditions like serum sickness and certain autoimmune diseases like systemic lupus erythematosus. Type 4 hypersensitivity: Also known as delayed-type hypersensitivity (DTH), this reaction involves the activation of T cells, particularly CD4+ T cells, which release cytokines and recruit inflammatory cells to the site of antigen exposure. It typically takes 24-72 hours to develop and is associated with conditions like contact dermatitis and some autoimmune diseases. 4/4