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Suppression of DNA synthesis in mitogen stimulated leukocytes with partial trypsin digests of Staphylococcus aureus
Abstract:
Staphylococcus aureus protein A (SPA) acts as a mitogen stimulating DNA synthesis and is not antagonistic to the mitogenic activity of other mitogens. The mitogenicity of SPA is due to the protein's multivalent Fc antibody receptors. Partial trypsin digestion of SPA yields monovalent Fc antibody receptors which are not mitogenic. Using a thymidine incorporation assay, results indicated that tryptic digests of SPA added to mouse splenic leukocytes 12 hours after stimulation with either concanavalin A, lipopolysaccaride or SPA suppressed the DNA synthesis normally elicited by these mitogens. SPA was digested with 1% trypsin at pH 8 for varying periods of time. As the digestion time increased from 0 to 60 minutes the mitogenicity of the SPA-trypsin digests decreased indicating cleavage from multivalent to monovalent SPA Fc antibody receptors. The decrease in mitogenicity of the SPA digests was directly associated with increased ability to inhibit DNA synthesis in mitogen stimulated leukocytes. A proposed mechanism for the inhibition of DNA synthesis suggests that SPA-monovalent Fc antibody receptors mimic cellular Fc receptor function thereby influencing cellular gene expression.
Insights
Staphylococcus aureus protein A (SPA) is a mitogen due to its multivalent Fc receptors. However, trypsin digestion yields monovalent receptors that inhibit DNA synthesis in stimulated leukocytes.
Area of Science:
- Immunology
- Molecular Biology
Background:
- Staphylococcus aureus protein A (SPA) is known to stimulate DNA synthesis, acting as a mitogen.
- SPA's mitogenic activity is attributed to its multivalent Fc antibody receptors.
Purpose of the Study:
- To investigate the role of SPA's Fc receptors in its mitogenic activity.
- To determine the effect of SPA Fc receptor valency on DNA synthesis in leukocytes.
Main Methods:
- SPA was subjected to partial trypsin digestion at pH 8 for varying durations.
- Mitogenicity was assessed using a thymidine incorporation assay.
- The effect of digested SPA on DNA synthesis in mitogen-stimulated mouse splenic leukocytes was evaluated.
Main Results:
- Partial trypsin digestion of SPA resulted in monovalent Fc antibody receptors, which lacked mitogenic activity.
- Tryptic digests of SPA suppressed DNA synthesis in leukocytes stimulated by concanavalin A, lipopolysaccharide, or SPA.
- A decrease in SPA mitogenicity correlated with an increased ability to inhibit DNA synthesis.
Conclusions:
- The mitogenicity of SPA is dependent on its multivalent Fc antibody receptors.
- Monovalent Fc receptors derived from SPA can inhibit DNA synthesis in stimulated leukocytes.
- SPA-monovalent Fc receptors may inhibit DNA synthesis by mimicking cellular Fc receptor function and influencing gene expression.