Nature of infectious diseases Flashcards
what is artificial acquired active immunity
Immunisation by artificial acquired active immunity is a process by which an individual is vaccinated with an antigen (usually a weakened or inactivated pathogen) to stimulate their immune system to produce an adaptive immune response against the pathogen. This immune response provides protection against future infections with the same pathogen.
The immunological basis of this process is the ability of the immune system to recognize and respond to foreign substances, such as pathogens, through the production of specific antibodies and immune cells. When a vaccine is administered, it contains a small amount of the pathogen or a part of the pathogen, such as a protein or a piece of its DNA. This exposure triggers the immune system to produce a response to the pathogen without causing disease.
The adaptive immune response to a vaccine involves the activation of B cells and T cells. B cells produce antibodies that can recognize and bind to the specific antigen presented in the vaccine. The antibodies can then neutralize the pathogen or mark it for destruction by other immune cells. T cells, on the other hand, can recognize and destroy infected cells and help to regulate the immune response.
Over time, the immune system generates memory B and T cells that can quickly recognize and respond to the pathogen if the individual is exposed to it in the future. This provides long-term protection against the pathogen and is the basis of acquired active immunity.
Explain virulence factors
Toxins are one of the most well-known virulence factors produced by pathogens. These molecules can cause damage to host cells by disrupting their membranes or interfering with their metabolic processes. Examples of toxins include the exotoxins produced by Staphylococcus aureus, which can cause toxic shock syndrome, and the endotoxins produced by Gram-negative bacteria, which can cause sepsis.
Enzymes are another type of virulence factor that can be produced by pathogens. These molecules can help the pathogen to invade host tissues or evade the host’s immune system. For example, the enzyme hyaluronidase, produced by some bacteria, can break down the extracellular matrix that surrounds host cells, allowing the bacteria to invade and spread through host tissues.
Adhesins are molecules produced by pathogens that help them to attach to host cells or tissues. This is an important step in the establishment of an infection. For example, the fimbriae produced by Escherichia coli help the bacteria to attach to the cells lining the urinary tract, leading to urinary tract infections.
Other virulence factors produced by pathogens include capsules, which can help the pathogen to evade the host’s immune system, and siderophores, which help the pathogen to acquire essential nutrients from the host.
The expression of virulence factors can be regulated by the pathogen in response to environmental cues or signals from the host. This allows the pathogen to adjust its virulence in response to changing conditions, such as the presence of immune cells or nutrients.
Virulence factors that damage the host
Toxins: Toxins are molecules that can cause damage to host cells by disrupting their membranes or interfering with their metabolic processes. There are two types of toxins: exotoxins and endotoxins. Exotoxins are produced by Gram-positive bacteria, such as Staphylococcus aureus, Streptococcus pyogenes, and Clostridium botulinum. Endotoxins are produced by Gram-negative bacteria, such as Escherichia coli and Salmonella typhi.
Enzymes: Enzymes produced by pathogens can cause damage to host cells and tissues by breaking down various components of the host’s cells. For example, hyaluronidase is an enzyme produced by Streptococcus pyogenes that can break down the extracellular matrix of the host’s tissues, allowing the bacteria to spread and cause damage.
Adhesins: Adhesins are molecules produced by pathogens that help them to attach to host cells or tissues. The attachment is a crucial step in establishing an infection. For example, fimbriae produced by Escherichia coli help the bacteria to attach to cells lining the urinary tract, leading to urinary tract infections.
Capsules: Capsules are structures that surround some bacteria and protect them from the host’s immune system. Capsules can prevent immune cells from recognizing the bacteria and can also prevent antibodies from binding to the bacteria. Examples of bacteria with capsules include Streptococcus pneumoniae and Haemophilus influenzae.
Biofilms: Biofilms are communities of bacteria that can attach to surfaces, including the host’s tissues. Biofilms can form on medical devices, such as catheters, and can cause infections that are difficult to treat.
Innate Defence against Infection
Physical and chemical barriers: The skin and mucous membranes act as physical barriers that prevent pathogens from entering the body. The acidity of the skin and mucous membranes also creates a chemical barrier that can kill or inhibit the growth of some pathogens.
Pattern recognition receptors (PRRs): PRRs are proteins on the surface of immune cells that can recognize patterns on pathogens called pathogen-associated molecular patterns (PAMPs). When PRRs recognize PAMPs, they trigger a signaling cascade that activates immune cells to respond to the infection.
Phagocytic cells: Phagocytic cells, such as macrophages and neutrophils, engulf and digest pathogens that have entered the body. They can also release cytokines and other signaling molecules that activate other immune cells.
Natural killer cells: Natural killer cells are a type of immune cell that can recognize and kill infected cells. They can also release cytokines that activate other immune cells.
Complement system: The complement system is a group of proteins in the blood that can identify and bind to pathogens. This can lead to the activation of the proteins, which can then destroy the pathogen or mark it for destruction by phagocytic cells.
The Adaptive Immune Response Against Infection
The adaptive immune response is a specialized defense mechanism that is activated when the innate immune system is not able to eliminate a pathogen. The adaptive immune response is highly specific to the pathogen and provides long-lasting protection against future infections. It involves the activation of immune cells called lymphocytes, which can recognize and respond to specific antigens on the surface of the pathogen. There are two types of lymphocytes involved in the adaptive immune response: B cells and T cells.
B cells produce antibodies, which are proteins that can recognize and bind to specific antigens on the surface of the pathogen. Once the B cell has recognized the antigen, it can divide and differentiate into plasma cells, which produce large amounts of antibodies, and memory B cells, which can quickly respond to future infections with the same pathogen. Antibodies can neutralize the pathogen by preventing it from entering host cells or by marking it for destruction by other immune cells, such as phagocytes.
T cells can recognize and respond to antigens that are presented to them by other immune cells, such as antigen-presenting cells (APCs). There are two types of T cells: helper T cells and cytotoxic T cells. Helper T cells can activate other immune cells, such as B cells and cytotoxic T cells, by releasing cytokines and other signaling molecules. Cytotoxic T cells can recognize and kill infected host cells by releasing toxic molecules.
