The innate immune response plays an important but unknown role in host defense against Mycobacterium tuberculosis. To define the function of innate immunity during tuberculosis, we evaluated M. tuberculosis replication dynamics during murine infection. Our data show that the early pulmonary innate immune response limits M. tuberculosis replication in a MyD88-dependent manner. Strikingly, we found that little M. tuberculosis cell death occurs during the first 2 weeks of infection. In contrast, M. tuberculosis cells deficient in the surface lipid phthiocerol dimycocerosate (PDIM) exhibited significant death rates, and consequently, total bacterial numbers were reduced. Host restriction of PDIM-deficient M. tuberculosis was not alleviated by the absence of interferon gamma (IFN-␥), inducible nitric oxide synthase (iNOS), or the phagocyte oxidase subunit p47. Taken together, these data indicate that PDIM protects M. tuberculosis from an early innate host response that is independent of IFN-␥, reactive nitrogen intermediates, and reactive oxygen species. By employing a pathogen replication tracking tool to evaluate M. tuberculosis replication and death during infection, we identify both host and pathogen factors affecting the outcome of infection. Phagocyte innate antimicrobial mechanisms are crucial in host defense against intracellular pathogens. For Mycobacterium tuberculosis and many other pathogens, interferon gamma (IFN-␥)-mediated activation of infected macrophages is central in controlling bacterial growth. Indeed, IFN-␥ is required to induce the majority of known macrophage effector functions, including the generation of reactive nitrogen and oxygen intermediates, phagosome-lysosome fusion, and autophagy (1). In the case of M. tuberculosis, antigen-specific CD4 ϩ T cells are the primary in vivo source of IFN-␥, but this adaptive immune response does not begin to develop until after 2 weeks postinfection (p.i.) (2). Whether innate immunity contributes to M. tuberculosis control prior to the arrival of antigen-specific T cells in the lung remains an outstanding question in the field.Recent work bearing on this question revealed that innate responses dependent on the central signaling molecule MyD88 are critical in defense against M. tuberculosis, as MyD88 Ϫ/Ϫ mice were highly susceptible despite normal adaptive immune responses (3). Moreover, human studies indicate that genetic variation in the innate immune response influences human susceptibility to tuberculosis (4). These observations suggest that innate immunity may play an important role in host defense against mycobacteria; however, the precise mechanisms remain unknown.To define the function of innate immunity in controlling M. tuberculosis growth, we monitored M. tuberculosis replication dynamics during murine infection. This previously validated technique (5) exploits an unstable plasmid as a replication clock, allowing bacterial replication and death rates to be determined from a simple differential plating technique. In this study, we apply this app...

Insulin-like growth factor (IGF) activity is regulated by six high affinity binding proteins (IGFBPs) and possibly by some of the nine IGFBP-related proteins (IGFBP-rPs). To determine the phylogenetic relationship of this proposed gene superfamily, we conducted maximum likelihood (ML) and Bayesian inference analyses on a matrix of amino acid sequences from a diversity of vertebrate species. A single most likely phylogram, ML bootstrap, and Bayesian consensus tree of 10,000,000 generations revealed a monophyletic IGFBP lineage independent of the IGFBP-rPs. The IGFBPs segregated into three distinct clades: IGFBP-1, -3, and -6. Subsequent gene duplication events within the IGFBP-1 and -3 clades resulted in the production and divergence of IGFBP-2 and -4 within the IGFBP-1 clade and IGFBP-5 in the IGFBP-3 clade. By contrast, the IGFBP-rPs were distributed paraphyletically into two clades: IGFBP-rP1, 5, and 6 in one clade and the CCN family (IGFBPrP2-4,7-9) in another. A recently identified IGFBP-3 homolog in rainbow trout localized to the IGFBP-2 subclade. Subsequence analysis identified a RGD motif common to IGFBP-2 orthologs, but did not identify the nuclear localization sequence present in IGFBP-3 and -5 homologs. The putative trout IGFBP-3 was 36-55% identical to different IGFBP-2 proteins, but only 24-27% identical to IGFBP-3 proteins. These results suggest that the IGFBPs and IGFBP-rPs are at best distantly related and that the limited similarities likely resulted from exon shuffling. They also suggest that rainbow trout, and possibly other salmonids, possess two IGFBP-2 paralogs as the putative trout IGFBP-3 is misannotated.