Microbiologist's Exam - Only The Best Can Pass

A bacterial infection involves the invasion of the body by harmful bacteria. When the immune system detects the presence of bacteria, it produces antibodies to fight against them. IgG is one of the major types of antibodies produced by the immune system in response to an infection. IgG antibodies are particularly effective against protein-based antigens, which are substances on the surface of bacteria that the immune system recognizes as foreign. Therefore, it is true that a bacterial infection involving a protein-based antigen would result in the activation of IgG antibodies.

The statement is false because myeloperoxidase pathways are dependent on the presence of oxygen. Myeloperoxidase is an enzyme found in certain white blood cells, and it requires oxygen to function properly. Without oxygen, the myeloperoxidase pathways cannot occur.

A positive tuberculin skin test indicates that a cell-mediated immune response has occurred. This is because a tuberculin skin test measures the delayed hypersensitivity reaction, which is mediated by T cells. These T cells recognize and respond to antigens from the tuberculosis bacteria, leading to inflammation at the site of injection. This response is characteristic of a cell-mediated immune response, which involves the activation of T cells and other immune cells to eliminate the pathogen.

Complement fixation refers to the binding of complement components by antigen-antibody complexes. This process occurs when antibodies bind to antigens, forming immune complexes. These immune complexes then activate the complement system, leading to the binding of complement components to the immune complexes. This binding can result in various immune responses, including inflammation, opsonization, and lysis of the antigen-antibody complexes.

Dendritic cells are the most effective antigen presenting cells. They have the ability to capture, process, and present antigens to T cells, initiating an immune response. Dendritic cells have specialized structures called dendrites that increase their surface area, allowing for efficient antigen uptake. They also express high levels of major histocompatibility complex (MHC) molecules, which are crucial for presenting antigens to T cells. Additionally, dendritic cells have the ability to migrate to lymphoid tissues, where they can interact with T cells and initiate an immune response.

The high ratio of IgM to IgG antibodies suggests that the patient's immune system is producing a primary immune response to the viral disease. This indicates that the patient has not encountered this organism previously, as a secondary immune response would be expected in that case.

Natural killer cells are able to kill virus-infected cells without prior sensitization. Unlike cytotoxic T cells, which require prior exposure to specific antigens, natural killer cells can recognize and kill infected cells without the need for prior sensitization. This ability allows natural killer cells to provide a rapid response to viral infections and play a crucial role in the innate immune system.

Paracrine chemical signals are released by cells and affect other cell types locally without being transported in the blood. Unlike hormones, which are transported through the bloodstream to target cells in distant parts of the body, paracrine signals act on nearby cells within the same tissue or organ. Autocrine chemical signals act on the same cells that release them, while neurotransmitters are chemical signals that transmit signals across synapses in the nervous system. Therefore, the correct answer is paracrine chemical signals.

Complement lyses cells by inserting complement proteins into the cell membrane. These complement proteins form a membrane attack complex (MAC) that creates pores in the cell membrane. These pores disrupt the integrity of the cell membrane, leading to the lysis or destruction of the cell. This mechanism is part of the immune response and helps to eliminate pathogens and infected cells from the body.

The complement system is a part of the immune system that helps in the elimination of pathogens. It can be activated through various pathways, including the binding of antibodies to antigens on the pathogen surface, the binding of lectins to the pathogen surface, and the creation of a local environment on the pathogen surface that allows complement activation. However, antibodies do not secrete cytokines. Cytokines are signaling molecules that help regulate immune responses, but they are not directly involved in complement activation. Therefore, "Antibody secretes cytokines" is not a pathway through which complement can be activated.

During an antibody response, macrophages play a crucial role in processing antigens and presenting them to other immune cells. Macrophages engulf and break down pathogens, such as viruses, into smaller fragments. These fragments are then displayed on the surface of the macrophage, allowing them to be recognized by other immune cells, such as T cells. This presentation of antigens by macrophages is essential for the activation of other immune cells and the initiation of an effective immune response against the pathogen.

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Antigen-presenting cells (APCs) play a crucial role in activating helper T cells. They do so by presenting antigens on their surfaces using major histocompatibility complex (MHC) molecules. Class II MHC antigens are specifically involved in presenting antigens to helper T cells. Therefore, APCs must express Class II MHC antigens on their surfaces to activate helper T cells. IgE and Gamma Interferon are not directly involved in antigen presentation, and Class I MHC antigens are involved in presenting antigens to cytotoxic T cells, not helper T cells.

CD3 is the correct answer because it is a protein that is necessary for signal transduction after an antigen binds with a T-cell. CD3 is a complex of proteins that is associated with the T-cell receptor (TCR) on the surface of T-cells. When an antigen binds to the TCR, CD3 helps to transmit the signal into the T-cell, initiating a cascade of events that ultimately leads to T-cell activation and the immune response. CD10, CD15, and CD1 are not directly involved in signal transduction after antigen binding.

C3a and C5a are complement proteins that are released during complement activation. These proteins are known as anaphylatoxins and are responsible for inducing inflammation. One of the main effects of C3a and C5a is increasing vascular permeability, which allows for the recruitment of immune cells to the site of infection or injury. This increased permeability allows for the leakage of fluid and proteins from blood vessels into the surrounding tissues, leading to swelling and redness. So, the correct answer is vascular permeability.

Passive immunization involves the administration of pre-formed antibodies, which provides immediate protection against a specific pathogen. This is in contrast to active immunization, where the body needs time to produce its own antibodies. Therefore, passive immunization is advantageous as it offers a more rapid response to an infection or disease.

All of the options mentioned in the question are related to immunogenicity. The age of the patient can affect the immune response, as the immune system may weaken with age. Protein structure plays a crucial role in determining the immunogenicity of a molecule, as certain structural features can trigger an immune response. The size of the molecule can also influence immunogenicity, as larger molecules may be more likely to be recognized by the immune system. Finally, the route of administration can impact the immune response, as different routes may result in varying levels of immune activation.

MHC Class I has one long alpha and a short beta
MHC Class II has an alpha chain and a beta chain of equal length

Each T-cell bears a TCR of only one specificity means that each T-cell has a T-cell receptor (TCR) that is specific to a particular antigen. This implies that T-cells are capable of recognizing and responding to a wide variety of antigens, as each T-cell carries a unique TCR that can bind to a specific antigen. This specificity is crucial for the immune response, as it allows T-cells to identify and target specific pathogens or abnormal cells in the body.

Oxygen-independent killing refers to the mechanisms by which immune cells can kill pathogens without the need for oxygen. The respiratory burst mechanism is a process in which immune cells produce reactive oxygen species (ROS) to kill pathogens. Therefore, it is not excluded from oxygen-independent killing. On the other hand, lysozyme, lactoferrin, and proteases are all examples of oxygen-independent killing mechanisms. Lysozyme breaks down bacterial cell walls, lactoferrin binds to iron and prevents bacterial growth, and proteases degrade bacterial proteins.

Chlorous Acid is not a product of oxygen-dependent myeloperoxidase-independent reactions. The other options, Singlet Oxygen, Hydrogen Peroxide, Hydroxyl Radical, and Superoxide Anion, are all end-products of these reactions.

Autocrine chemical signals are released by cells and have a local effect on the same cell type that released them. This means that the chemical signal acts on the same cells that secreted it, influencing their own behavior or regulating their own functions. Unlike paracrine signals, which act on nearby cells of a different type, or hormones, which are released into the bloodstream to act on distant target cells, autocrine signals have a more localized effect within the same cell population. Neurotransmitters, on the other hand, are chemical signals that transmit signals between nerve cells in the nervous system.

Type II Hypersensitivities - Antibody binds to antigens on self cells and complement is activated
Type III Hypersensitivities - Antibodies bind free antigens and move to tissues and then complement is activated

TLR (Toll-like Receptors) is an example of a PRR (pattern recognition receptor) of the innate immune system. PRRs are proteins that recognize specific patterns on pathogens and trigger an immune response. TLRs are a group of PRRs that are located on the surface of immune cells and recognize various pathogen-associated molecular patterns (PAMPs). They play a crucial role in initiating the innate immune response by recognizing and binding to these PAMPs, leading to the activation of downstream signaling pathways and the production of inflammatory cytokines.

Oxygen-dependent myeloperoxidase-dependent and myeloperoxidase-independent reactions both involve the production of reactive oxygen species (ROS) as part of the immune response. Superoxide anion is a type of ROS that is generated in both types of reactions. It is produced by various enzymes and plays a role in oxidative stress and inflammation. Therefore, superoxide anion is the shared product in both types of reactions.

A T-dependent antigen refers to an antigen that requires the assistance of T cells to initiate an immune response. Proteins are known to be T-dependent antigens because they can activate T cells and stimulate the production of specific antibodies. Water, polysaccharides, and cholesterol are not typically classified as T-dependent antigens as they do not elicit a strong T cell response.

Hypochlorous acid is an end-result of oxygen-dependent myeloperoxidase-dependent reactions. Myeloperoxidase is an enzyme found in white blood cells that catalyzes the reaction between hydrogen peroxide and chloride ions, resulting in the formation of hypochlorous acid. Hypochlorous acid is a potent oxidant and antimicrobial agent that plays a crucial role in the immune response, particularly in killing bacteria and other pathogens.

Detoxification processes can break down superoxide anions generated by respiratory burst mechanisms. One of the products of this reaction is hydrogen peroxide.

The explanation for the answer "False" is that immunoglobulin classes are actually determined by the constant region of the heavy chain, but the subclasses are determined by the variable region of the heavy chain. The constant region of the light chain does not play a role in determining the immunoglobulin classes or subclasses.

Hereditary angioedema is a disorder characterized by rapid swelling of the tissue. This condition is caused by an overproduction of a complement protein called C2b. Complement proteins are part of the immune system and play a role in inflammation and immune response. In the case of hereditary angioedema, the excessive production of C2b leads to the swelling of tissues, particularly in the face, hands, feet, and airways.

A B lymphocyte can switch its immunoglobulin heavy-chain class after binding to its specific antigen. This is known as class switching and it allows the B lymphocyte to produce antibodies of different isotypes, such as IgM, IgG, IgA, etc. Class switching is an important mechanism in the immune response as it allows for the production of antibodies with different effector functions to combat different types of pathogens.

The affinity for antigen refers to the strength of the binding between an antibody and its target antigen. This property is determined by the variable region of the antibody, specifically the antigen-binding site. The heavy-chain constant region, on the other hand, is responsible for other functions such as isotype (class) determination, ability to fix complement, and ability to cross the placenta. Therefore, the affinity for antigen is not dependent on the structure of the heavy-chain constant region.

The intracellular killing pathways mentioned in the options are Nitric Oxide Dependent Killing, Oxygen Dependent Myeloperoxidase-Independent Killing, Oxygen Independent Killing, and Oxygen Dependent Myeloperoxidase-Dependent Killing. The correct answer states that all of these pathways are intracellular killing pathways, indicating that options B, C, and D are correct.

All IgG molecules are composed of two identical heavy and two identical light chains, since the B cell that makes the immunoglobulin only expresses one heavy and one light chain. Thus, an IgG could not have both a kappa and a lambda chain

The genes rearrange before exposure to the antigen

Class I MHC proteins are cell surface proteins that are present on virtually all cells. They play a crucial role in the immune response by presenting antigens to cytotoxic T cells, which then destroy the infected cells. Class I MHC proteins are codominantly expressed, meaning that both copies of the gene are expressed equally. However, they do not utilize recombination to generate diversity. Instead, diversity in class I MHC proteins is generated through a process called antigen processing and presentation, where a wide range of antigens can be presented on the cell surface.