The response of Acropora digitifera to ocean acidification is determined using geochemical proxy measurements of the skeletal composition of A. digitifera cultured under a range of pH levels. We show that the chemical composition (d 11 B, Sr/Ca, Mg/Ca, and Ba/Ca) of the coral skeletons can provide quantitative constraints on the effects of seawater pH on the pH in the calcification fluid (pH CF ) and the mechanisms controlling the incorporation of trace elements into coral aragonite. With the decline of seawater pH, the skeletal d 11 B value decreased, while the Sr/Ca ratio showed an increasing trend. The relationship between Mg/Ca and Ba/Ca versus seawater pH was not significant. Inter-colony variation of d 11 B was insignificant, although inter-colony variation was observed for Ba/Ca. The decreasing trend of pH CF calculated from d 11 B was from *8.5, 8.4, and 8.3 for seawater pH of *8.1, 7.8, and 7.4, respectively. Model calculations based on Sr/Ca and pH CF suggest that upregulation of pH CF occurs via exchange of H ? with Ca 2? with kinetic effects (Rayleigh fractionation), reducing Sr/Ca relative to inorganic deposition of aragonite from seawater. We show that it is possible to constrain the overall carbonate chemistry of the calcifying fluid with estimates of the carbonate saturation of the calcifying fluid (X CF ) being derived from skeletal Sr/Ca and pH CF (from d 11 B). These estimates suggest that the aragonite saturation state of the calcifying fluid X CF is elevated by a factor of 5-10 relative to ambient seawater under all treatment conditions.

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28HLA-G is involved in maternal-fetal immune tolerance and is reported to be a natural 29 tolerogenic molecule. Seven-spliced isoforms including dimeric and β2m-free forms 30 have been identified. The major isoform, HLA-G1 (and its soluble type HLA-G5), binds

HLA-G is a natural tolerogenic molecule and has the following unique features: seven isoforms (HLA-G1 to HLA-G7), formation of disulfide-linked homodimers, and β2-microglobulin (β2m)-free forms. Interestingly, individuals null for the major isoform, HLA-G1, are healthy and expressed the α2 domain-deleted isoform, HLA-G2, which presumably compensates for HLA-G1 function. However, the molecular characteristics of HLA-G2 are largely unknown. In this study, we unexpectedly found that HLA-G2 naturally forms a β2m-free and nondisulfide-linked homodimer, which is in contrast to the disulfide-bonded β2m-associated HLA-G1 homodimer. Furthermore, single-particle analysis, using electron microscopy, revealed that the overall structure and domain organization of the HLA-G2 homodimer resemble those of the HLA class II heterodimer. The HLA-G2 homodimer binds to leukocyte Ig-like receptor B2 with slow dissociation and a significant avidity effect. These findings provide novel insights into leukocyte Ig-like receptor B2-mediated immune regulation by the HLA-G2 isoform, as well as the gene evolution of HLA classes.