The Journal of Immunology, 2006, 176: 3857.
Copyright © 2006 by The American Association of Immunologists
Response to Comment on "Cutting Edge: TLR4 Deficiency Confers Susceptibility to Lethal Oxidant Lung Injury"
Xuchen Zhang and
Patty J. Lee
Section of Pulmonary and Critical Care Medicine, Yale University School of Medicine, New Haven, CT 06520
Doctors Kubo and Ishizawa raise two issues regarding our studies demonstrating the increased susceptibility of TLR4–/– hyperoxic lung injury (1). The first issue raised is the fact that C3H/HeJ mice, which have mice to defective TLR4 expression, are resistant to hyperoxia (2), which suggests that TLR4 deficiency should confer resistance rather than susceptibility to hyperoxia. In our hands, we also find C3H/HeJ to be resistant to hyperoxia. However, others have already shown that there are important differences in the pulmonary responses between C3H/HeJ and TLR4–/– mice, such as the responses to ozone and fly ash (3). Genetic analyses of C3H/HeJ mice have identified multiple genes, other than TLR4, that are potentially altered and linked to susceptibility patterns (4, 5). Our recent studies demonstrating the decreased survival of TLR4–/– mice, as well as TLR2/4–/– mice to hyperoxia, further support the concept that TLR-independent pathways may account for the resistant phenotype observed in C3H/HeJ mice (1, 6).
Drs. Kubo and Ishizawa present BAL protein data to support their claim that TLR4 deficiency confers resistance to hyperoxia. Our primary endpoint was survival, so it is difficult to interpret their data in the absence of survival rates. Furthermore, what is the control group for their TLR4–/– mice? TLR4–/– mice that originate from Dr. S. Akira are on a mixed genetic background (C57BL6/129). We have maintained the mixed background and therefore used wild-type C57BL6/129 as controls, as reported previously (7).
The second issue raised is that our wild-type mice had better survival rates compared with previous reports. As alluded to above, given that the mouse genetic strain is important in determining susceptibility to hyperoxia (2, 8) and the articles they quote use C57BL/6 mice, a comparison would be invalid. Furthermore, survival rates in hyperoxia may vary even within the same strain. For example, one group has published survival rates in hyperoxia for wild-type C57BL/6 mice that range from 2 to 6.75 days (9, 10, 11). Other groups report wild-type survival as 5–7 days (12, 13). Therefore, even if we discount the issue of mouse strain, our wild-type survival of 3.5–6.5 days is consistent with the literature. We sincerely believe that our studies highlight novel functions for TLRs in acute lung injury but as pointed out by Drs. Kubo and Ishizawa, additional investigations will be required to fully understand the role of TLR4 in oxidant injury.
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