Regulation Of The Immune Response

Front 1

When the immune system encounters an antigen, one of two outcomes may develop:

Back 1

immunity or tolerance

Front 2

Give three examples of Ag regulation of the immune response

Back 2

1. Antigen concentration (very large doses often inhibit the immune response and cause tolerance)
2. Chemical nature of the antigen (Protein Ag --> humoral and cell-mediated immune responses. Non-protein Ag --> mainly IgM Abs)
3. Portal of entry (Protein administered subcutaneously or intradermally is carried to local LNs by Langerhans cells, where the response is initiated. Ag given IV or orally can cause tolerance, possibly due to rapid elimination.)

Front 3

If an animal is immunized with a specific antigen and is injected with preformed antibody to that same antigen just before or within 5 days after antigen priming, the immune response to the antigen is reduced up to 100-fold. Why?

Back 3

Ab feedback inhibition: Antibodies eliminate the antigen they were produced against, thereby removing the initiating stimulus for antigen-reactive B cell clonal expansion.

Front 4

Immune complexes trapped by FDCs are crucial in the selection of BCs that express high-affinity BCRs (during the process of affinity maturation in Ab responses to T-dep Ag). However, immune complexes can also be inhibitory rather than enhancing. Explain how

Back 4

Ag-Ab complexes can simultaneously bind to BCR [via Ag] and the CD32 [FcgammaRIIB] via the Fc portion of the Ab.
This cross-linking of receptors causes phosphatases associated with the cytoplasmic tail of the FcR to inhibit signaling by the BCR complex and block naive B cell activation.