The HLA-G message is alternatively spliced into multiple transcripts, two of which encode soluble isoforms. To initiate studies on the specific functions of the soluble isoforms, we produced soluble rHLA-G1 (rsG1) and rsG2 in human embryonic kidney 293 cells and characterized the proteins. Both isoforms were glycosylated and formed disulfide-bonded oligomers. Recombinant sG1 associated with β2-microglobulin, whereas rsG2 did not. Mouse mAb generated to rsG1 (1-2C3), which identified exclusively sG1, and mAb generated to rsG2 (26-2H11), which identified both soluble and membrane G2 (m/sG2), were used for immunohistochemical isoform mapping studies on placental tissue sections. Soluble G1 protein was abundant in many subpopulations of trophoblast cells, whereas m/sG2 protein was present exclusively in extravillous cytotrophoblast cells. Although both isolated placental villous cytotrophoblast cells and chorion membrane extravillous cytotrophoblast cells contained mRNAs encoding sG1 and sG2, protein expression was as predicted from the immunostains with m/sG2 present only in the invasive trophoblast subpopulation. Analysis of function by Northern and Western blotting demonstrated that both rsG1 and rsG2 inhibit CD8α expression on PBMC without changing CD3δ expression or causing apoptotic cell death. Collectively, the studies indicate that: 1) both sG1 and m/sG2 are produced in placentas; 2) transcription and translation are linked for sG1, but not G2; 3) expression of G2 is exclusively associated with the invasive phenotype; and 4) the two isoforms of sG may promote semiallogeneic pregnancy by reducing expression of CD8, a molecule required for functional activation of CTL.

In these studies, we examined the role of elaborations for subjects learning a procedural skill (viz., using a personal computer) from an instructional text. In Experiment 1, we compared two sources of elaborations: those provided by the author and those generated by learners while reading. In the latter condition, subjects were given advance information about the tasks they were to perform so that they would generate more specific task-related elaborations while reading. Each source of elaborations facilitated skill performance. This result contrasts with results of the past experiments testing declarative knowledge in which author-provided elaborations were found to hurt performance. In Experiment 2, the author-provided elaborations were classified into those illustrating the syntax of the operating system commands and those explaining basic concepts and their applicability. Syntax elaborations produced significant facilitation for experienced and novice computer users. Concept elaborations produced no reliable improvement.An important question to both memory theorists and pedagogists is, "What variables will improve the learning and retention of written information?" One such variable that has been the topic of considerable speculation and research is the effect of elaborations (J. R. Anderson & Reder, 1979;Bransford, 1979;Chiesi, Spilich, & Voss, 1979;Craik & Tulving, 1975;Mandl & Ballstaedt, 1981;Mandl, Schnotz, & Tergan, 1984;Reder, 1976Reder, , 1979Weinstein, 1978). In the view of most researchers, there are several reasons why elaborations should help subjects learn and remember the main ideas of a text. Elaborations provide multiple retrieval routes to the essential information by creating more connections to the learner's prior knowledge. If one set of connections is forgotten, it may be possible to retrieve the desired information another way. Furthermore, if the learner forgets an important point, it may be possible to reconstruct it from the information that is still available.Elaborations can arise from two distinct sources: first, the text itself can contain elaborations of the main ideas, and second, the reader can generate them independently while reading. We use the same term for both types, because we define elaborations as any information that supports, clarifies, or further specifies the main points of a text. Elaborations can take many forms, including examples, details, analogies, restatements, and deductions.

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