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Enhancement of in Vivo and in Vitro Murine Immune Responses by the Cyclophosphamide Metabolite Acrolein¹

Departments of Pharmacology and Toxicology and Biostatistics, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298-0613

Cyclophosphamide (CY)-mediated immunoenhancement has been attributed to the inhibition of suppressor T-cell generation. In order to exert its effects on the immune system, metabolic activation of CY is required. The metabolite of CY responsible for its immunoenhancing properties are not known. Two reactive metabolites of CY which may inhibit suppressor T-cell generation are phosphoramide mustard and acrolein, compounds known to primarily bind to DNA and sulfhydryl groups, respectively. The objective of this study was to determine whether acrolein and/or phosphoramide mustard are capable of enhancing the immune response in a manner similar to CY. Administration of 100 µmol/kg of acrolein, i.v., to female C57BL/6 x C3H F₁ mice 1 day before antigen exposure (sheep red blood cells) resulted in a 50% increase in the delayed-type hypersensitivity response (foot pad swelling). The Day 4 primary humoral immune response to sheep red blood cells was also increased by 88 and 60% after the administration of 30 and 100 µmol/kg acrolein 1 day before sensitization with sheep red blood cells. Exposure of splenocyte cultures to 3 x 10^-7 and 10^-6 M 4-hydroperoxy-CY or acrolein produced significant increases in the in vitro T-dependent antibody-forming cell response. In contrast, the antibody-forming cell response of cultures exposed to 3 x 10^-8-10^-4 M phosphoramide mustard did not increase above control levels. These results suggest that acrolein is responsible for the CY-induced enhancement of the immune response. Moreover, the enhancement may be produced by the binding of acrolein to sulfhydryl groups of molecules of cells required for the generation of suppressor T-cells.

¹ Supported in part by USPHS Grants ES05317 and ES03434 and National Institute of Environmental Health Sciences Contract ES55094.

² To whom requests for reprints should be addressed, at Box 613, Medical College of Virginia, Richmond, VA 23298-0613. Recipient of a National Research Service Award Postdoctoral Fellowship ES05317.

Received 6/23/87. Revised 9/23/87. Accepted 9/28/87.