Micro Dr Sloma Questions

Negative selection of immature B cells refers to the process where B cells that recognize self antigens are eliminated or signaled to undergo programmed cell death (apoptosis). This is an important mechanism to prevent the development of B cells that could potentially attack the body's own tissues (autoimmunity). By eliminating self-reactive B cells, the immune system ensures that only B cells capable of recognizing foreign antigens are allowed to mature and participate in immune responses.

Rickettsia sp., Coxiella sp., and Chlamydia sp. all have an obligate requirement for growth within host cells. This means that they cannot grow and replicate outside of a host cell and are dependent on the host cell's machinery for their survival and reproduction.

β-hemolysis refers to the complete lysis of red blood cells in the media. This is caused by the organism producing a hemolysin, which is a toxin that specifically targets and lyses red blood cells. As a result, the media around the colony appears clear because the red blood cells have been completely lysed.

The growth of the Gram-positive rod on tellurite agar indicates that the organism is Corynebacterium diphtheriae. This is because Corynebacterium diphtheriae is the only organism among the options that is known to produce tellurite reductase, an enzyme that allows it to reduce tellurite and grow on tellurite agar. This characteristic is used as a diagnostic test for identifying Corynebacterium diphtheriae.

Th2 T cells exert their effector functions through the secretion of IL-4 and IL-5. These cytokines play a crucial role in the activation and recruitment of other immune cells, particularly B cells and eosinophils. IL-4 promotes the differentiation of B cells into antibody-producing plasma cells, while IL-5 stimulates the production and activation of eosinophils, which are involved in the defense against parasitic infections and allergic reactions. Therefore, the secretion of IL-4 and IL-5 by Th2 T cells is essential for the immune response against certain pathogens and the regulation of allergic responses.

The correct answer is "The blood used in chocolate agar has been heated." This is because chocolate agar is made by heating sheep blood to inactivate certain enzymes that could interfere with the growth of bacteria. Heating the blood also helps release nutrients that are essential for bacterial growth. This process is important in creating a suitable environment for bacterial culture and identification in the laboratory.

The correct answer describes the organisms growing in the patient's blood culture as saprophytic organisms found in the soil or intestinal tract of humans and animals. This suggests that the organisms are likely to be normal flora or opportunistic pathogens that have entered the bloodstream.

The presence of Gram+ cocci in chains suggests the presence of Streptococcus spp. The presence of Gram‐positive bacilli suggests the presence of Corynebacterium spp. The presence of Gram‐negative cocci suggests the presence of Neisseria spp. Therefore, Neisseria spp., Streptococcus spp., and Corynebacterium spp. could be growing in her specimen.

Dark field microscopy is a technique that allows for the visualization of organisms that are difficult to see using traditional bright field microscopy. Borrelia sp., the bacteria responsible for Lyme disease, is a spirochete that is better visualized using dark field microscopy due to its thin, helical shape. This technique allows for the visualization of the organism's characteristic motility and helps in the identification of Borrelia sp. Therefore, dark field microscopy is a more accurate method for visualizing Borrelia sp. compared to a Gram stain.

During T cell development, immature T cells with receptors that associate with self major histocompatibility complex (MHC) with adequate affinity are selected to mature. This selection process ensures that T cells are able to recognize and respond to antigens presented by self MHC molecules. T cells that do not have receptors that associate with self MHC or have receptors with too high or too low affinity for self MHC are signaled to undergo apoptosis, preventing the development of T cells that may cause autoimmune reactions. This process is crucial for the proper functioning of the immune system.

T cells require CD28:B7 co-stimulation and IL-2 cytokine signaling in addition to the recognition of specific peptides presented by MHC in order to undergo activation, proliferation, and differentiation. CD28:B7 interaction provides a co-stimulatory signal that enhances T cell activation, while IL-2 is a crucial cytokine that promotes T cell proliferation and survival. Therefore, both CD28:B7 co-stimulation and IL-2 cytokine signaling are necessary for T cell activation and subsequent immune response.

The causative agent of the infection was able to establish active infection due to the failure to generate Th1 T cells. Th1 T cells play a crucial role in cell-mediated immunity and are responsible for activating macrophages to kill intracellular pathogens, such as Mycobacterium tuberculosis (the causative agent of tuberculosis). Without Th1 T cell activation, the immune response is impaired, allowing the infection to persist and cause symptoms such as fevers, night sweats, weight loss, and a productive cough with bloody sputum.

Vaccines containing killed pathogens or antigenic components (subunits like peptides) do not enter host cells. Hence, they induce a B cell-mediated humoral response. On the other hand, live ATTENUATED LIVE VACCINES do penetrate cells, eliciting a cell-mediated immune response against intracellular antigens. SO FOR INTRACELLULAR ORGANISMS, LIVE ATTENUATED VACCINES ARE MORE EFFECTIVE!

Inactivated Vaccines:
Inactivated vaccines, as the name implies, can produce a protective immune response without the risk of infection by the agent. They are used for agents that cannot be attenuated, that may cause recurrent infection, or that have ONOGENIC POTENTIAL.

A defect in the expression of CD19 and Igβ molecules on the surface of a B cell would prohibit B cell activation. CD19 is a co-receptor that plays a crucial role in B cell signaling and activation, while Igβ is a component of the B cell receptor complex that is essential for antigen recognition and signaling. Therefore, a defect in the expression of these molecules would impair the ability of B cells to respond to antigens and initiate an immune response.