Antigen structural requirements for immunoglobulin isotype switching in mice

Area of Science:

• Immunology
• Molecular Biology

Background:

• L-Tyrosine-p-azobenzene-p-arsonate (RAT) is a known immunogenic carrier.
• Bifunctional antigens like DNP-SAC-RAT elicit weak, IgM-only antibody responses in mice.
• The spacer length and carrier epitope number influence immune responses.

Purpose of the Study:

• To investigate the effect of a trifunctional antigen (DNP-SAC-RAT-PRO(9)-RAT; TRI) on antibody production.
• To determine the minimum structural requirements for inducing IgG plaque-forming cell (PFC) responses.
• To explore the role of anti-prolyl antibodies in immune responses.

Main Methods:

• Synthesis of trifunctional antigen TRI and bifunctional antigens BI-2 and BI-3.
• Immunization of A/J mice with various antigens (RAT, BI-1, TRI, BI-2).
• Measurement of IgM and IgG plaque-forming cell (PFC) responses.

Main Results:

• TRI induced approximately twice as many PFCs as BI-1 and elicited both IgM and IgG PFCs in secondary responses.
• TRI induced IgG PFC responses in mice primed with RAT, BI-1, or keyhole limpet hemocyanin, while BI-1 did not.
• Priming with acetyl-(proline)10-L-tyrosine-p-azobenzene-p-arsonate followed by boosting with BI-2 induced IgG PFCs, suggesting a role for anti-prolyl antibodies.

Conclusions:

• A minimum of two carrier epitopes per antigen molecule is required for IgG induction.
• Priming with a mono-epitope carrier (RAT) is sufficient for IgG responses to a trifunctional immunogen.
• Synergistic T helper cell activity is likely involved in immunoglobulin isotype switching.