Microbiology Chapter 13

What is the third line of defense in the immune system?

Adaptive immunity, which is acquired after an immunizing event such as an infection.

What are the roles of B and T lymphocytes in adaptive immunity?

They undergo a selective process to react specifically to one antigen or immunogen.

Define immunocompetence.

The ability of the body to react with countless foreign substances.

What are antigens?

Molecules that can be seen and identified by the immune system.

What distinguishes immunogens from antigens?

Immunogens are antigens that provoke a response from the immune system.

What is an epitope?

The portion of an antigenic molecule to which a lymphocyte responds.

List the four stages of a specific immune response.

1. Lymphocyte development and clonal deletion; 2. Presentation of antigen and clonal selection; 3. Challenge of B and T lymphocytes by antigens; 4. T-lymphocyte response and B-lymphocyte response.

What is the Major Histocompatibility Complex (MHC)?

A set of genes that codes for human cell markers or receptors, vital for immune recognition.

What are the three classes of MHC genes?

Class I (on all nucleated cells), Class II (on immune regulatory cells), Class III (involved with the complement system).

What is the role of CD molecules in the immune response?

CD molecules, or clusters of differentiation, are involved in various immune responses, with over 400 identified.

How do B cells respond to antigens?

When activated, B cells divide and differentiate into plasma cells that release antibodies.

What is the function of Helper T cells?

They activate macrophages, assist B-cell processes, and help activate cytotoxic T cells.

What do Cytotoxic T cells do?

They lead to the destruction of infected host cells and other foreign cells.

What is the role of Regulatory T cells?

They control the T-cell response by secreting anti-inflammatory cytokines.

What is the significance of memory cells in the immune response?

Memory cells ensure future reactivity to a specific antigen.

Describe the maturation process of B cells.

B cells mature in specialized bone marrow sites and migrate to lymphoid organs.

Describe the maturation process of T cells.

T cells mature in the thymus gland, directed by thymic hormones.

What is the primary function of lymphocyte receptors?

To accept or grasp antigens in some form.

What is the difference between B cell receptors and T cell receptors?

B cell receptors bind free antigens, while T cell receptors bind processed antigens complexed with MHC molecules.

What initiates the inflammatory response when pathogens cross the first line of defense?

Resident macrophages migrate to the site and ingest the pathogen.

What are antigen presenting cells (APCs)?

Cells such as macrophages, dendritic cells, or B cells that ingest pathogens and present antigens to T and B lymphocytes.

What is the role of cytokines in T cell function?

Cytokines help destroy pathogens but T cells do not produce antibodies.

How do antibodies function in the immune response?

Antibodies attach to specific antigens, marking them for destruction or neutralization.

What is the significance of lymphocyte recirculation?

B and T cells constantly recirculate through the circulatory system and lymphatics to enhance immune surveillance.

What are CD3 receptors?

CD3 receptors surround the T-cell receptor and assist in binding.

What is the role of CD4 coreceptors?

CD4 coreceptors help the T-cell receptor bind to MHC II molecules on antigen-presenting cells (APCs).

What do CD8 coreceptors do?

CD8 coreceptors are found on cytotoxic T cells and bind to MHC I molecules.

Where do B cells develop?

B cells develop in the bone marrow.

What is the process of lymphocyte homing?

Naïve lymphocytes circulate in the blood, 'homing' to specific sites in lymph nodes, spleen, and other lymphoid tissues.

What initiates B-cell development?

Stromal cells in the bone marrow provide chemical signals that initiate B-cell development.

How is immunologic diversity generated in B and T cells?

Diversity is generated by rearrangement of gene segments that code for antigen receptors.

What is an immunoglobulin (Ig)?

Immunoglobulin is a large glycoprotein that serves as the antigen receptor of B cells and, when secreted, functions as antibodies.

What are the components of an immunoglobulin structure?

Immunoglobulins consist of antigen binding sites, variable regions, light chains, heavy chains, and constant regions.

What is clonal selection?

Clonal selection is the mechanism by which the correct B or T cell is activated by an incoming antigen.

What is clonal expansion?

Clonal expansion is the rapid multiplication of B or T cell clones after activation by an antigen.

What is clonal deletion?

Clonal deletion is the process by which potentially problematic lymphocyte clones that react to self are destroyed during development.

What is an immunogen?

An immunogen is a substance that can elicit an immune response and must meet certain requirements such as foreignness and size.

What types of substances can act as immunogens?

Whole microbes, cells from other humans or animals, complex proteins, and certain polysaccharides can act as immunogens.

What are haptens?

Haptens are small foreign molecules that cannot elicit an immune response by themselves but can become immunogenic when linked to a larger carrier molecule.

What are alloantigens?

Alloantigens are cell surface markers that occur in some members of the same species but not in others, such as blood group antigens.

What are superantigens?

Superantigens are bacterial toxins that activate T cells at a much higher rate than ordinary antigens, potentially leading to severe immune responses.

What is the role of antigen presenting cells (APCs)?

APCs process antigens and present them to T lymphocytes, essential for T cell activation.

Which cells are considered antigen presenting cells?

Macrophages, B cells, and dendritic cells are all antigen presenting cells.

What is cell-mediated immunity (CMI)?

CMI involves T-cell reactions and is characterized by the complexity and diversity of T cell responses.

What dictates the actions of T cells?

The actions of T cells are dictated by the antigen presenting cells (APCs) that activate them.

What is required for T cells to be activated?

Some type of MHC (self) recognition.

What is the main function of T Helper (TH) cells?

To regulate immune reactions to antigens and activate macrophages.

How do T Helper cells activate macrophages?

Directly by receptor contact or indirectly by releasing cytokines such as interferon gamma (IFNγ).

What are Cytotoxic T (TC) cells designed to do?

Kill other cells, including virally infected cells, cancer cells, and foreign cells.

What mechanism do TC cells use to kill target cells?

They secrete perforins to create holes in cell membranes and granzymes to digest proteins of the target cell.

What distinguishes Gamma-Delta T cells from other T cells?

They have T-cell receptors that recognize a wide range of antigens and respond quickly, bridging nonspecific and specific immune responses.

What are Natural Killer (NK) cells?

Cells that lack specificity for antigens and are among the first to attack cancer and virus-infected cells.

What is the structure of an antibody?

A symmetrical Y-shaped arrangement with antigen-binding fragments (Fabs) and a crystallizable fragment (Fc).

What is the function of the hypervariable region of an antibody?

It is the site where the epitope binds, allowing for specificity in antigen binding.

What role does the Fc fragment of an antibody play?

It binds to receptors on cell membranes, activating functions such as opsonization.

What is opsonization?

The process where attachment of an antibody to foreign cells is followed by binding of the Fc portion to phagocytes.

What is the primary function of IgA?

To provide specific immunity against pathogens in mucous membranes and serous secretions.

What does IgG represent in the immune response?

It is the most prevalent antibody, predominant in secondary immune responses.

What is the difference between active and passive immunity?

Active immunity involves the individual's own immune response, while passive immunity involves receiving antibodies from another source.

What is a titer?

The level of antibodies in the serum over time.

What are the two major categories of vaccines?

Live attenuated and inactivated (or killed) vaccines.

What is herd immunity?

A form of indirect protection from infectious diseases that occurs when a large percentage of a population becomes immune.

What are the four types of acquired immunity?

Natural immunity, artificial immunity, active immunity, and passive immunity.

What is the role of memory B and T cells?

They are created from clones activated by a specific antigen and provide long-term immunity.

What happens during B-cell activation?

B cells are activated by antigens and can produce antibodies specific to those antigens.

What is the significance of colostrum in immunity?

It is high in IgA and provides passive immunity to newborns by coating their gastrointestinal tract.

What is the function of IgE?

To stimulate basophils and mast cells, causing the release of histamine and other agents of inflammation and allergy.

What is the primary antibody produced during the primary immune response?

IgM.

What is the role of the Fc portion of antibodies?

It activates complement and enhances phagocytosis through opsonization.

What is the relationship between antigens and memory cells?

Exposure to a particular antigen can lead to the creation of memory cells that are chemically related to it.

What is convalescent serum?

Serum containing antibodies from people who recovered from SARS-CoV-2.

What was the first recorded attempt at immunization?

In 6th century China, smallpox scabs were dried, ground, and blown into the nostrils of vulnerable individuals.

What is variolation?

Deliberate inoculation of dried pus from smallpox pustules into the arm of a healthy person.

Who introduced variolation to England?

Lady Montagu in 1721.

Who is Edward Jenner and what did he do?

He developed the smallpox vaccine in 1796 by using material from cowpox lesions.

What is the definition of vaccination?

Any immunity obtained by inoculation with selected antigens.

What is passive immunization?

Transfer of antibodies from one individual to another, such as using horse serum for tetanus.

What is gamma globulin?

Immunoglobulin extracted from pooled blood of human donors, used to treat specific infections.

What is the purpose of vaccination?

To stimulate a primary response and a memory response for future exposure to pathogens.

What are the qualities of an effective vaccine?

Protects against natural pathogens, has low side effects, stimulates immune response, and produces lasting effects.

What are whole cell or virus vaccines?

Vaccines that use live, attenuated cells or viruses, or killed cells/inactivated viruses.

What are conjugated vaccines?

Subunits of pathogens conjugated with proteins to enhance immunogenicity.

What are DNA vaccines?

Vaccines that insert microbial DNA into plasmids, which are taken up by human cells to produce proteins.

What are mRNA vaccines?

Vaccines that instruct cells to produce a viral spike protein, prompting an immune response.

What are common routes of vaccine administration?

Subcutaneous, intramuscular, intradermal, nasal, and oral.

What is an adjuvant?

A substance that enhances the immunogenicity of a vaccine.

What are common side effects of vaccines?

Local reactions at the injection site, fever, allergies, and other adverse reactions.

What rare reactions can occur from vaccines?

Panencephalitis from measles vaccine, back-mutation in polio vaccine, and neurological effects.

What did the Institute of Medicine conclude about the MMR vaccine and autism?

There is no causal link between the MMR vaccine and autism.

Who should be cautious with live vaccines?

Immunocompromised individuals and pregnant patients.

What is the revised recommendation for adult vaccinations?

Vaccination to boost older immunizations and protect against adult infections.

What diseases still lack functional vaccines?

Malaria, HIV/AIDS, diarrheal diseases, respiratory diseases, and certain worm infections.

What is the significance of vaccine trials?

Vaccines must undergo extensive trials to ensure safety before being licensed for general use.

What is the impact of not being vaccinated?

Outbreaks of diseases like measles and mumps can occur, decreasing herd immunity.

What is the role of memory cells in vaccination?

Memory cells provide a rapid and robust immune response upon re-exposure to the pathogen.

What is the goal of vaccine development?

To create effective vaccines for diseases that currently lack them and improve global health.