ratti infection at days 10 or 31 post-L. major infection (Figure 2d, e). The comparison of the L. major-specific humoral response revealed also no difference in single and co-infected mice (Figure 3a–e). Especially L. major-specific IgG2b that is associated with a Th1 response was not suppressed but even slightly increased by S. ratti co-infection (Figure 3d). Taken together, these results suggest that a pre-existing nematode infection

did not interfere with the generation of a protective cellular and humoral type-1 response to L. major but increased pro-inflammatory responses in general. Subsequent L. major infection, in contrast, partially suppressed the Th2 polarization induced by pre-existing S. ratti infection. Therefore, we asked whether this changed nematode-induced production of Th2 cytokines would affect clearance of S. ratti infection in these co-infected mice. First, we compared the larval output in the faeces of S. ratti singly and S. ratti/L. major Alvelestat co-infected mice by

quantitative PCR (Figure 4a). Despite the changed cytokine response, S. ratti/L. major co-infected mice displayed the same larval output with comparable kinetics until the faeces was negative for S. ratti DNA indicating complete clearance of nematode infection (Figure 4b). Re-infection of S. ratti single and S. ratti/L. major co-infected mice with S. ratti again led to similar PARP inhibitor larval output that was reduced in comparison with the first infection indicating efficient memory generation (data not shown). Nevertheless, the suppression of nematode-induced Th2 responses by the pro-inflammatory responses elicited by L. major co-infection (Figure 2b, c) strongly suggests that worm expulsion could be affected if L. major infection preceded nematode infection. To prove this hypothesis, we performed co-infection experiments in reversed order. Mice were infected with a high Cyclooxygenase (COX) dose of L. major and 14 days later, when L. major-specific Th1 response was established, mice were co-infected with S. ratti iL3 (Figure 5a). Comparison of the larval output in the faeces (Figure 5b) as well as numbers of parasitic adults in the gut (Figure 5c) did not reveal impaired

or delayed clearance of S. ratti infection in co-infected mice. We did observe an increased output of L1 in co-infected mice at the maximum of infection that was not significant (Figure 5b, day 8 p.i.). As neither the kinetics of worm clearance nor the worm burden in the intestine showed significant differences, we chose to analyse the underlying immune responses (Figure 6a). Strikingly, no suppression of CD3-induced or S. ratti antigen-specific proliferation, IL-10 and IL-13 response were observed in this experimental set-up in co-infected mice (Figure 6b–d). Also, the absent IFN-γ response in S. ratti-infected mice was not restored by pre-existing L. major infection (Figure 6e). Finally, no change in the S. ratti-specific humoral response was observed upon co-infection (Figure 6f, g).