Stage and tissue expression profiles of Ixodes ricinus cysteine and aspartic peptidases. Messenger RNA levels of individual enzymes were determined by semi-quantitative two-step RT PCR. Panel A: Expression of peptidase mRNAs in whole body homogenates of I. ricinus eggs, unfed larvae, unfed nymphs, males, unfed females and females attached for 1 day on the guinea pigs. Panel B: Expression of peptidase mRNAs in tissues dissected from partially engorged females (the 5-th day of feeding). The abbreviations used are as in the text. IrFer shows the mRNA amplification of tick ferritin used as template loading control. (For details, see Methods).