In wt mice significant levels of SIgA were observed locally in the nasal and lung lavages, but also in the peripheral vaginal lavages after i.n. BLP-SV administration, while mice vaccinated i.m. with SV alone showed decreased or absent SIgA levels (Fig. 3A). In contrast to the levels observed in JQ1 wt mice, low to absent SIgA levels
were measured in nasal (Fig. 3B) and vaginal (Fig. 3C) lavages in TLR2KO mice. In addition, very low levels of SIgA antibodies were measured in mucosal lavages when SV alone was administered either i.n. or i.m. The data show that local and peripheral SIgA production after i.n. BLP-SV administration depends on the interaction of BLP with TLR2. Next, we explored if the observed enhanced IAV-specific B-cell response after i.n. BLP-SV vaccination in wt mice compared BI 6727 solubility dmso to TLR2KO mice as shown in Fig. 1 also affected IAV-specific systemic antibody production. We observed an enhanced IAV-specific IgG response in serum of wt mice
after booster vaccination with i.n. BLP-SV in contrast to vaccinated TLR2KO mice, which resembles the IgG response of the SV vaccine in wt mice (Fig. 4A and B). Then, we investigated if IgG class switch to IgG1 or IgG2c after i.n. BLP-SV vaccination also depended on TLR2 interaction. Here, we showed that the BLP-SV-induced class switch to IgG2c depended on the interaction of BLP with TLR2 (Fig. 4C). In contrast, the IAV-specific IgG1 response was not reduced in TLR2KO mice compared to wt control mice (Fig. 4D). We therefore suggest that the increase in IgG1 in the TLR2KO mice after both i.n. BLP-SV and SV immunization might indicate an inhibitory role for TLR2 on class switch to IgG1. Thus, both IAV-specific systemic Th1 cell and subsequent B-cell responses that were associated with enhanced
IgG2c antibody production induced after i.n. BLP-SV vaccination depended on interaction of BLP with TLR2. Earlier studies have demonstrated in vitro that BLPs can activate TLR2 signalling in human TLR-transfected HEK cells and mouse dendritic cells . This implies that TLR2 activation by BLP could be responsible for enhancing adaptive immune responses in vivo, but formal proof for this was lacking. Previous studies showed that the effect of TLR2 triggering on the outcome of the immune second response in vivo is variable and depends on several unknown factors: TLR2 can form heterodimers with other TLRs, specifically TLR1 and TLR6  and  and TLR2 is expressed by a plethora of immune cells , , , ,  and . Furthermore, the immunostimulatory activity of BLPs in vivo could be the result of activation of innate receptors different from TLR, for example, NOD receptors. Here, we provided clear evidence for an essential role of TLR2 in the BLP-dependent activation of the IAV-specific adaptive immune responses in vivo upon nasal vaccination. Moreover, we showed that both local and systemic IAV-specific IFN-? T-cell (Fig. 1A and C) and B-cell responses (Fig.