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A letter to the editor related to blood transfusion published in a previous 2006 issue is presented.

The existing estimates of the recombination fraction between DR and DP are quite variable and often based on anecdotal observations. We have estimated the DR/DP crossover frequency on the basis of families typed for HLA markers and GLO. The frequency of DR/GLO crossing over was 8.7% (23/264 informative meioses), maternal recombinations being about twice as frequent as paternal ones. Of 17 DR/GLO recombinant families typed for DPw1-6, DP was informative in 11 (13 recombinations) but only one of these gave rise to a DR/DP crossover. According to these data the DR/DP recombination fraction is below 1%, in contrast to some earlier published materials. HLA-DR/DP haplotypic associations on 127 informative Caucasoid haplotypes have been evaluated. In agreement with previous studies, DR3 was positively associated with DPw1 and, in addition, DR7 was found to be positively associated with DP-blank (not DPw1-6). The rare DPw6 allele is possibly associated with the DR4, Dw14 allele. The DR-DP haplotype profiles suggest other associations which might become significant if larger materials are tested. The frequency of DP alleles in a random material (N = 201) was found to be in accordance with most of the previously published frequences on European Caucasoids with DPw4 as the predominating frequency (gene frequency 40%) and a blank frequency of 27%.

An enzyme that hydrolyzes soman (1,2,2-trimethylpropyl methylphosphonofluoridate) and two other phosphonofluoridates, but does not hydrolyze DFP (diisopropylphosphorofluoridate), has been partially purified from a rod-shaped spore-forming gram-positive OT (obligate thermophilic) bacterium. The enzyme shows a marked Mn2+ stimulation, and in this and its substrate preference does not resemble the organophosphorus acid anhydrolase (sometimes termed DFPase) found in squid. Like the squid enzyme, it is not inhibited by mipafox (N,N'-diisopropylphosphordiamidofluoridate), is not inactivated by ammonium sulfate, and does hydrolyze the acetylcholinesterase-inhibitory pair of diastereoisomers of soman as well as the relatively noninhibitory pair, thus detoxifying soman. In these three properties the OT enzyme does not resemble the ubiquitous organophosphorus acid anhydrolase often purified from mammalian and bacterial sources by cold ethanol fractionation. Thus this phosphono-specific OT enzyme may have a natural substrate and a physiological role distinct from other organophosphorus acid anhydrolases.

LB-Q1 and LB-Q4 are two subtypes of DRw52, defined by proliferative T-cell clones. These subtypes represent a polymorphism of the DR beta III gene. Similar subtypes of DRw52 can be defined by oligonucleotide typing, serology and RFLP analysis. In the present study we compared these typing techniques on a panel of 22 HLA-D homozygous, DRw52-positive typing cells. All typing techniques correlated very well. Three subtypes of DRw52 could be identified. Our results show that typing for cellularly defined structures can be done with a variety of noncellular techniques. This observation has important implications for matching in unrelated bone marrow transplantation and for disease association studies.

HLA typing of an HLA-B/GLO recombinant family using bulk-expanded DP(SB) alloreactive T-cells (GNN1 to 6) as well as conventional HLA-ABC, D, DR, and DQ typing showed that a paternal recombination had taken place between HLA-DR and DQ on the one hand and HLA-DP(SB) on the other. The recombinant child was DPw4,6-heterozygous and differed in terms of class II determinants only for DPw6 from two otherwise HLA identical siblings, who were probably DPw4/4-homozygous. These siblings did not stimulate the recombinant in MLC whereas they responded to his cells indicating that DPw6 can stimulate in primary MLC. Moreover, it was possible to generate and bulk-expand DPw6-reactive lymphocytes (PLs) between MT and MA as responders and BN as stimulator. The correlation coefficient (r) between the reaction of these PLs and the GNN6 (anti-DPw6) reagents was 1.0 when tested against a panel of 71 individuals. This is the first report demonstrating that the DPw6 gene, like the DPw1-w5 genes, is located between DR/DQ and GLO. The frequency of the DPw6 antigen in 41 unrelated, randomly selected Danes was 7%. HLA-DP typing of the BN family revealed that the DPw6 positive but not DPw6 negative family members gave intermediate responses with one (GNN2B) but not with another (GNN2A) anti-DPw2-reagent. Studies of 63 healthy individuals (unrelated to the BN family) revealed seven similar discrepancies between GNN2A and GNN2B. Strikingly, all four DPw6 positive stimulators gave rise to such discrepancies indicating that the GNN2B reagent is cross-reactive and recognize a common part of the DPw2 and DPw6 molecules. No cases of GNN2A+/GNN2B- stimulators were found.

The polymorphism of HLA class II molecules in man is particularly evident when comparisons between population groups are made. This study describes a DR3 haplotype commonly present in the American black population. Unlike the Northern European population, in which almost all DR3 individuals are DQw2, approximately 50% of DR3-positive American blacks express a DQw4 allelic product. This study characterizes the DR subregion of that haplotype. cDNA sequence analysis has revealed a DR beta gene which differs at several positions from previously described DR3 beta 1 genes. It is postulated that a gene-conversion-like event with a DRw52 beta gene as donor has generated some of these differences. The haplotype carries a DRw52a allele as defined by oligonucleotide hybridization studies. DNA restriction fragment analysis using a family and several unrelated individuals has allowed us to identify DR alpha and beta fragments associated with the DR3(w18),DQw4 haplotype. The most striking observation is that the DR3(w18),DQw4 haplotype differs from DR3(w17),DQw2 haplotypes at multiple class II loci. Several genetic mechanisms including reciprocal recombination, gene conversion, and point mutation were involved in generating the differences between these haplotypes. Once established, the DR3(w18),DQw4 haplotype appears to be relatively stable in the population.

Lymphocytes from highly selected donors were primed for 10 days and subsequently bulk-expanded in IL 2 (TCGF) containing cultures. Two well-discriminatory PLT (CDP = Copenhagen DP) reagents against each of the DPw1-w6 specificities and one against each of the two "new" specificities, CDP4s and CDPHEI, were selected for further studies. Three combinations made in two recombinant families and four of ten HLA-A, B, and DR compatible combinations discriminated well in contrast to seven of 46 DR compatible, but HLA-A or B incompatible combinations. All reagents gave highly reproducible results, and high correlations (r-values between 0.73-1.00) for DP assignments were obtained with CDP and GNN reagents. No triplets were found for the DPw1-w6 and CDP HEI specificities. The "new" specificity CDP HEI defined in an HLA-DR/GLO recombinant family gave a coefficient of correlation with GNN 8 of 0.91. Another "new" specificity, CDP4s constitutes a subgroup ("split") of DPw4. The gene frequencies of DPw1-w6 estimated in 102 unrelated randomly selected Danes agreed with those reported for other Caucasoid populations. The gene frequencies CDP HEI and CDP4s were 0.03 and 0.08, respectively. The associations between DR3-DPw1, DR2-DPw4, and DRw6-DPw2 were confirmed. It is concluded that DP-typing with bulk-expanded reagents is a reliable and so far the only technique which can reveal the polymorphism of the DP gene products.

Human lymphocytes, 10 days after treatment with phytohemagglutinin P (PHA-P), show PLT (secondary in vitro restimulation) reaction patterns which correspond to their cellular (HLA-D) type. Lymphocytes with shared cellular type stimulate PHA primed cells to a lesser degree than the majority of lymphocytes with unshared HLA-D type, which stimulate a strong response. Using a standard 3H thymidine incorporation technique, it is possible to detect responses in as early as 12 hr total incubation time, although usually a 22-48 hr total incubation time is normally required. This method is simple, gives results that correspond to the primary mixed leukocyte response, and thus may be useful as a cross-matching technique for cadaveric renal transplantation.