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Classical pathway
Classical pathway The mechanism of complement activation initiated by antigen-antibody aggregates and proceeding by way of C1, C4 and C2.
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Mechanism
The arrangement or association of the elements or parts of anything in relation to the effect they generate; the combination of mental processes by which an effect is generated.
Complement
A series of serum proteins involved in the mediation of immune reactions. The complement cascade is triggered classically by the interaction of antibody with specific antigen.
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Clasp
Device that retains a removable partial denture to stationary teeth.
Clasped thumbs and mental retardation
A syndrome with the following characteristic features: (1) neurologically: mental retardation and aphasia (lack of speech); (2) limbs: adducted (clasped) thumbs, absent extensor pollicis longus and/or brevis muscles to the thumb, shuffling gait, and leg spasticity; (3) growth: small body size; (4) skeleton: lumbar lordosis (sway back). The syndrome is inherited as an X-linked trait and so affects mainly boys. Alternative names include MASA syndrome (MASA stands for mental retardation, aphasia, shuffling gait, and adducted thumbs), adducted thumb with mental retardation, congenital clasped thumb with mental retardation, and the Gareis-Mason syndrome.
Class I MHC molecules
Proteins encoded by genes in the major histocompatibility complex (q.v.). Class I molecules are designated HLA-A, B, or C.
Class II MHC molecules
Proteins encoded by genes in the major histocompatibility complex (q.v.). Class II molecules are designated DP, DQ or DR.
Class switch
See isotype switch.
Classical conditioning
Elicitation of a response by a stimulus that normally does not elicit that response. The response is one that is mediated primarily by the autonomic nervous system (such as salivation or a change in heart rate). A previously neutral stimulus is repeatedly presented just before an unconditioned stimulus that normally elicits that response. When the response subsequently occurs in the presence of the previously neutral stimulus, it is called a conditioned response, and the previously neutral stimulus, a conditioned stimulus.
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Cell-mediated cytotoxicity (CMC)
Killing (lysis) of a target cell by an effector lymphocyte.
Cell-mediated immunity (CMI)
Immune reaction mediated by T cells; in contrast to humoral immunity, which is antibody mediated. Also referred to as delayed-type hypersensitivity.
Class I MHC molecules
Proteins encoded by genes in the major histocompatibility complex (q.v.). Class I molecules are designated HLA-A, B, or C.
Class II MHC molecules
Proteins encoded by genes in the major histocompatibility complex (q.v.). Class II molecules are designated DP, DQ or DR.
Class switch
See isotype switch.
Classical pathway
Clonal deletion
The loss of lymphocytes of a particular specificity due to contact with either "self" or artificially introduced antigen.
Clonal selection theory
The prevalent concept that specificity and diversity of an immune response are the result of selection by antigen of specifically reactive clones from a large repertoire of preformed lymphocytes, each with individual specificities.
Cluster determinant (CD)
Cluster of antigens with which antibodies react that characterize a cell surface marker.
Combinatorial joining
The joining of segments of DNA to generate essentially new genetic information, as occurs with Ig genes during the development of B cells. Combinatorial joining allows multiple opportunities for 2 sets of genes to combine in different ways.
Complement
A series of serum proteins involved in the mediation of immune reactions. The complement cascade is triggered classically by the interaction of antibody with specific antigen.
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