It is tempting to speculate that the ’ideal’ dosage for the combination therapy of anti-CD40 IgG4 and anti-CD40L PAS-Fab may fall within the range between the high (promoting fungal infections in all animals) and low dosages (permitting humoral rejection and recalcitrant pleural effusions) administered in the current study group. Here, CD40 is linked to fungal infectious disease.