Polymorphism of the human C3b/C4b receptor. Identification of a third allele and analysis of receptor phenotypes in families and patients with systemic lupus erythematosus.

We have isolated C3bR from surface-labeled erythrocytes of 180 normal individuals and 45 patients with SLE. These studies have identified a previously unrecognized C3bR molecule on E with a Mr of approximately 160,000 daltons on nonreduced SDS-polyacrylamide gels. A similar receptor phenotype is also found on other C3bR-bearing peripheral blood leukocytes. Family studies demonstrate that this approximately 160,000-dalton molecule represents a third allele that is inherited in a codominant fashion at the same locus as the two previously described C3bR alleles. In unrelated normal donors a common allele (A) determines an approximately 190,000-dalton C3bR (gene frequency 0.83), a second allele (B) determines an approximately 220,000-dalton C3bR (gene frequency = 0.16), and a third rare allele (C) determines an approximately 160,000-dalton C3bR (gene frequency = 0.01). There were no major differences in gene frequencies among Caucasians and blacks or normal individuals and patients with SLE. However, compared with normal individuals, heterozygous C3bR-AC patients with SLE express large amounts of the approximately 160,000-dalton C3bR on E. Expression of C3bR molecules among heterozygous siblings is similar, suggesting that an inherited factor controls expression of the two molecules in heterozygous donors. These observations constitute an instructive example of a structural polymorphism of an integral membrane glycoprotein and provide a structural and genetic basis for further molecular and functional analyses of C3bR in normal and patient populations.

Optical implementation of a single-iteration thresholding algorithm with applications to parallel data-base/knowledge-base processing.

Threshold (or relative magnitude) search is traditionally performed iteratively in a bit-serial manner in optical data-base/knowledge-base machines, which results in an execution time proportional to the operand size. We present a single-step threshold search algorithm and its optical implementation. The proposed algorithm performs magnitude comparison in constant time, independent of the operand size, and consequently it greatly increases the performance of optical data-base/knowledge-base processing operations such as searching, selection, retrieving, and sorting.

Optical content-addressable parallel processor for high-speed database processing.

We extend the concept of optical content-addressable parallel processing [Appl. Opt. 31, 3241 (1992)] to a novel architecture designed specifically for the parallel and high-speed implementation of database operations called optical content-addressable parallel processor for relational database processing (OCAPPRP). An OCAPPRP combines a parallel model of computation, associative processing, with parallel and high-speed technology optics. The architecture is developed to provide optimal support for high-speed parallel equivalence (pattern matching) and relative-magnitude searches (greater than and lesser than). Distinctive features of the proposed architecture include (1) a two-dimensional match-compare unit for two-dimensional pattern matching, (2) constant-time retrieval of database entries, (3) an optical word and bit-parallel relative-magnitude single-step algorithm, and (4) the capability of constanttime sorting. Since relational database operations rely heavily on parallel equivalence or relativemagnitue searches, database processing is an excellent candidate for implementation on an OCAPPRP. The architecture delivers a speedup factor of n over conventional optical database architectures, where n is the number of rows in a database table. We present an overview of the architecture followed by its optical implementation. The representative relational database operations, intersection, and selection are outlined to illustrate the architecture's potential for efficiently supporting high-speed database processing.

Constant-time parallel sorting algorithm and its optical implementation using smart pixels.

Sorting is a fundamental operation that has important implications in a vast number of areas. For instance, sorting is heavily utilized in applications such as database machines, in which hashing techniques are used to accelerate data-processing algorithms. It is also the basis for interprocessor message routing and has strong implications in video telecommunications. However, high-speed electronic sorting networks are difficult to implement with VLSI technology because of the dense, global connectivity required. Optics eliminates this bottleneck by offering global interconnects, massive parallelism, and noninterfering communications. We present a parallel sorting algorithm and its efficient optical implementation. The algorithm sorts n data elements in few steps, independent of the number of elements to be sorted. Thus it is a constant-time sorting algorithm [i.e., O(1) time]. We also estimate the system's performance to show that the proposed sorting algorithm can provide at least 2 orders of magnitude improvement in execution time over conventional electronic algorithms.

Polymorphism of the C3b/C4b receptor (CR1): characterization of a fourth allele.

The receptor for C3b/C4b (C3bR or CR1) has an unusual polymorphism in which three codominant alleles determine variants with a large difference in Mr (160,000, 190,000, or 220,000). We found an individual who has, in addition to the common 190,000 Mr molecule, a C3bR whose Mr is 250,000. In this proband and in some members of his family, this novel heterozygous phenotype can be isolated from 125I surface-labeled cells by iC3 or iC4 affinity chromatography or by immunoprecipitation with the use of polyclonal or monoclonal anti-C3bR. Relative to the 190,000 Mr C3bR, E from individuals in this family have 20 to 30% of the total receptor counts in the 250,000 Mr C3bR. However, on C3bR-bearing leukocytes there is a much larger amount of the 250,000 Mr C3bR (approximately 60%) relative to the 190,000 Mr C3bR. Similar to the other three C3bR variants, the Mr is 5,000 greater on polymorphonuclear cells than on E, and treatment of this new C3bR with endoglycosidase F decreases its Mr by approximately 10,000. Therefore, because this variant is inherited and has structural and functional similarities to the other three C3bR, we conclude that this 250,000 Mr CR1 probably represents a fourth allele.

Identification of the glycosaminoglycan-attachment site of mouse invariant-chain proteoglycan core protein by site-directed mutagenesis.

The invariant chain (Ii), a nonpolymorphic glycoprotein that associates with the immunoregulatory Ia proteins encoded by the major histocompatibility complex, has a proteoglycan form (Ii-CS) that bears a chondroitin sulfate glycosaminoglycan. In this proteoglycan form, Ii may remain associated with Ia at the cell surface. Inhibitors that prevent the addition of glycosaminoglycan to Ii have been found to depress antigen-presenting function. Ii does not have multiple candidate glycosaminoglycan-attachment sites, and we used site-directed mutagenesis to replace a candidate serine glycosaminoglycan-acceptor site with alanine at position 201 in the murine Ii protein. Transfection of the normal or altered gene into Ii-negative COS-7 cells showed that equivalent amounts of core Ii protein and its acidic, terminally glycosylated forms were synthesized, but the Ala-201 mutant Ii did not give rise to Ii-CS. The mutant protein had apparently normal transport through the Golgi compartment and associated stably with Ia molecules. Thus, this mutation directly identifies the site of glycosaminoglycan addition and shows that it can be eliminated without adversely affecting the overall biosynthesis of Ii.

Stable expression of cytolytic activity by influenza virus-specific cytotoxic T lymphocytes.

Influenza-specific immune cytotoxic T lymphocyte (CTL) populations maintain a constant level of in vitro cytolytic activity. This is demonstrable with both heterogeneous populations of anti-viral CTL from immune donors and long-term CTL clones derived from primed CTL precursors. Cytolytic machinery is stably expressed by these CTL populations under a variety of in vitro cultivation conditions. This finding is in contrast to results with alloreactive CTL generated by stimulation of primed CTL precursors that lose cytolytic activity on a per cell basis with time after stimulation. The results indicate that virus-specific, cloned CTL that stably express cytolytic activity are representative of the heterogeneous populations from which they are derived and further suggest a qualitative difference in the regulation and expression of cytolytic machinery between heterogeneous populations of influenza-specific CTL and alloreactive CTL.