Medroxyprogesterone, immunosuppression, and conceptus size in Peromyscus.

Area of Science:

• Immunology
• Reproductive Biology
• Mammalian Physiology

Background:

• The maternal immune system typically rejects foreign tissue, including allografts and fetuses.
• Progestins are known to modulate immune responses during pregnancy.

Purpose of the Study:

• To investigate the effects of exogenous medroxyprogesterone acetate (MPA) on skin transplant survival in mice.
• To determine if MPA influences conceptus size and weight during pregnancy.

Main Methods:

• Daily injections of MPA were administered to deer mice (Peromyscus maniculatus) and oldfield mice (Peromyscus polionotus).
• Skin allografts and transspecific grafts were transplanted and survival times recorded.
• Fetal and placental sizes and weights were measured in MPA-treated pregnant mice.

Main Results:

• MPA significantly extended the survival of both allografts and transspecific skin grafts in P. maniculatus.
• Allografts were retained longer than transspecific grafts in MPA-treated mice.
• MPA administration did not significantly alter near-term fetal or placental size and weight.

Conclusions:

• Exogenous MPA demonstrates immunosuppressive properties, enhancing allograft survival.
• MPA's lack of effect on conceptus size suggests its role in immune tolerance may not directly impact fetal development.
• Progestins might play a crucial role in preventing maternal immune rejection of the allogeneic conceptus.