Since a reduction in the IgG1/IgG2a ratio is associated with the development of a T H 1 response and protection against Brucella infection, IgG, IgG1 and IgG2a levels were characterized in TLR2, TLR4 and MyD88 following aerosol exposure (Figure 5 , panel F). The results reveal a significant contribution of TLR4 and MyD88 to IgG1 production and the importance of TLR2 and MyD88 to IgG2a production. Examination of the IgG1/IgG2a ratio suggests the dependence of a protective T H 1 response on expression of MyD88 and TLR2, but not TLR4. This is not a totally unexpected result since the Brucella LPS, and/or TcpB primarily exert their influence on TLR4-based signaling. The contribution of MyD88 and TLR2 to protective immune response as determined by the reduced bacterial burden in selected tissues is borne out in previous discussion. To reiterate, MyD88 −/− exhibits significant delays in clearance from all three tissues examined; TLR2 and TLR4 contribute to clearance from the lung alone.