Microbiology chapter 27

Phagocytes are primary effector cells for ____ _____

innate immunity

Lymphocytes (T and B cells) are primary effector cells for ____ _____

adaptive immunity

The adaptive immune system is subdivided into two branches which are highly dependent on each other:

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Cellular response (T cell–mediated immunity)

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Humoral response (antibody–mediated immunity)

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Goal of both branches is the same:Eliminate an identified antigen and remember it so that next time adaptive responses are faster

Immune responses

As a result of immune memory, antigen re-exposure triggers a much stronger secondary response

T Cell Selection and Clonal Deletion

Immature T cells undergo a two-step selection process to (1) select cells that recognize self antigens (positive selection) and (2) eliminate cells that react too strongly with self antigens (negative selection).

Immunogens and antigen binding

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Antigens are substances that react with antibodies or TCRs

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Not all antigens are immunogens(substances that induce an immune response)

Active immune response: generated from exposure to an antigen

Active immunity develops memory cells, producing a long-lasting immunity

Passive immune response: transfer of antibodies or immune cells

Passive immunity consists of pre-formed antibodies or cells and has a rapid effect, but doesn’t confer lasting immunity

Antibodies or immunoglobulins (Igs)

-IgG is the most common antibody circulating in the body

-Antibodies have two light and two heavy chains. Light and heavy chain makeup an antigen-binding site.

Initial antigen exposure (primary antibody response)

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Produces short-lived plasma cells that live for less than a week

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Produce mostly IgM, which rises in the blood, as measured by antibody titer

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Detecting IgG to a particular antigen indicates the patient has been exposed to that antigen

Later exposures (secondary antibody responses)

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Memory cells do not need T cell help for activation

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Antibody response is quicker

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Produces 10 to 100 times more antibody (mostly IgG)

IgM heavy chain

One each of the V, D, and J segments is recombined at random to form a functional heavy-chain gene

Kappa light chain

Randomly recombined V and J segments form a complete light-chain gene.

T Cell Receptors: Proteins, Genes, and Diversity

T cells do not interact with a foreign antigen unless it is presented in the context of an MHC protein

T Cell Subsets and Their Functions

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Th1 subset activates macrophages

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Th2 subset plays a crucial role in B cell activation and antibody production