Introduction:  The CD40/CD40L co-stimulatory pathway is an important mediator of rejection in tissue transplantation. However, the requirement of donor versus recipient CD40 has not been characterized. We utilized CD40-/- knockout (K0) mice as both donors and recipients to establish the requirement of CD40 in the rejection process.

Methods:  Sciatic nerve grafts were transplanted from either wild type CD40-/- KO  or wild type (WT) BALB/c mice into a subcutaneous pocket on the back of either CD40-/- KO or wild type C57BL/6 recipient mice. Following a 14 day recovery, recipient mice were sacrificed and their spleens and brachial lymph nodes were harvested. Splenocytes and nodal cells were stimulated with donor alloantigens and resultant production of interferon gamma (INF- gamma), and interleukins (IL)-5, -4, and –2 were quantified using the ELISPOT technique. 

Results: WT into WT nerve allografting produced robust cytokine responses (see table). When CD40-/- KO mice were used as either donors or recipients there was a reduction in cytokine production. However, when CD40-/- mice were used as donors and recipients there was a dramatic reduction in all cytokine levels compared to the other groups.

Conclusion:  When CD40-/- KO mice are used as donors or recipients there is only a partial blockade of the co-stimulatory pathway resulting in moderately reduced cytokine production. However, when CD40-/- KO donors and recipients, there is a profound reduction in cytokine production likely the result of complete costimulatory pathway blockade. This data suggests that CD40 is important in both donor and recipient.

Cytokine production in wild type mice compared to CD40-/- knockout mice