The invasion, provenance and diversity of Vespa velutina Lepeletier (Hymenoptera: Vespidae) in Great Britain

The yellow-legged or Asian hornet (Vespa velutina colour form nigrithorax) was introduced into France from China over a decade ago. Vespa velutina has since spread rapidly across Europe, facilitated by suitable climatic conditions and the ability of a single nest to disperse many mated queens over a large area. Yellow-legged hornets are a major concern because of the potential impact they have on populations of many beneficial pollinators, most notably the western honey bee (Apis mellifera), which shows no effective defensive behaviours against this exotic predator. Here, we present the first report of this species in Great Britain. Actively foraging hornets were detected at two locations, the first around a single nest in Gloucestershire, and the second a single hornet trapped 54 km away in Somerset. The foraging activity observed in Gloucestershire was largely restricted to within 700 m of a single nest, suggesting highly localised movements. Genetic analyses of individuals from the Gloucestershire nest and the single hornet from Somerset suggest that these incursions represent an expansion of the European population, rather than a second incursion from Asia. The founding queen of the Gloucestershire nest mated with a single male, suggesting that sexual reproduction may have occurred in an area of low nest density. Whilst the nest contained diploid adult males, haploid ‘true’ males were only present at the egg stage, indicating that the nest was detected and removed before the production of queens. Members of the public reported additional dead hornets associated with camping equipment recently returned from France and imported timber products, highlighting possible pathways of incursion. The utility of microsatellites to inform surveillance during an incursion and the challenge of achieving eradication of this damaging pest are discussed.

A Half-Century of Studies on a Chromosomal Hybrid Zone of the House Mouse

The first natural chromosomal variation in the house mouse was described nearly 50 years ago in Val Poschiavo on the Swiss side of the Swiss-Italian border in the Central Eastern Alps. Studies have extended into neighboring Valtellina, and the house mice of the Poschiavo-Valtellina area have been subject to detailed analysis, reviewed here. The maximum extent of this area is 70 km, yet it has 4 metacentric races and the standard 40-chromosome telocentric race distributed in a patchwork fashion. The metacentric races are characterized by highly reduced diploid numbers (2n = 22-26) resulting from Robertsonian fusions, perhaps modified by whole-arm reciprocal translocations. The races hybridize and the whole Poschiavo-Valtellina area can be considered a "hybrid zone." The studies of this area have provided insights into origin of races within hybrid zones, gene flow within hybrid zones and the possibility of speciation in hybrid zones. This provides a case study of how chromosomal rearrangements may impact the genetic structure of populations and their diversification.

Genetic differentiation within and away from the chromosomal rearrangements characterising hybridising chromosomal races of the western house mouse (Mus musculus domesticus)

The importance of chromosomal rearrangements for speciation can be inferred from studies of genetic exchange between hybridising chromosomal races within species. Reduced fertility or recombination suppression in karyotypic hybrids has the potential to maintain or promote genetic differentiation in genomic regions near rearrangement breakpoints. We studied genetic exchange between two hybridising groups of chromosomal races of house mouse in Upper Valtellina (Lombardy, Italy), using microsatellites. These groups differ by Robertsonian fusions and/or whole-arm reciprocal translocations such that F1 hybrids have a chain-of-five meiotic configuration. Previous studies showed genetic differentiation in two chromosomes in the chain-of-five (10 and 12) close to their centromeres (i.e. the rearrangement breakpoints); we have shown here that the centromeric regions of the other two chromosomes in the chain (2 and 8) are similarly differentiated. The internal chromosomes of the chain (8 and 12) show the greatest differentiation, which may reflect pairing and recombination properties of internal and external elements in a meiotic chain. Importantly, we found that centromeric regions of some non-rearranged chromosomes also showed genetic differentiation between the hybridising groups, indicating a complex interplay between chromosomal rearrangements and other parts of the genome in maintaining or promoting differentiation and potentially driving speciation between chromosomal races.

Large-scale structure of brown rat (Rattus norvegicus) populations in England: effects on rodenticide resistance

The brown rat (Rattus norvegicus) is a relatively recent (<300 years) addition to the British fauna, but by association with negative impacts on public health, animal health and agriculture, it is regarded as one of the most important vertebrate pest species. Anticoagulant rodenticides were introduced for brown rat control in the 1950s and are widely used for rat control in the UK, but long-standing resistance has been linked to control failures in some regions. One thus far ignored aspect of resistance biology is the population structure of the brown rat. This paper investigates the role population structure has on the development of anticoagulant resistance. Using mitochondrial and microsatellite DNA, we examined 186 individuals (from 15 counties in England and one location in Wales near the Wales–England border) to investigate the population structure of rural brown rat populations. We also examined individual rats for variations of the VKORC1 gene previously associated with resistance to anticoagulant rodenticides. We show that the populations were structured to some degree, but that this was only apparent in the microsatellite data and not the mtDNA data. We discuss various reasons why this is the case. We show that the population as a whole appears not to be at equilibrium. The relative lack of diversity in the mtDNA sequences examined can be explained by founder effects and a subsequent spatial expansion of a species introduced to the UK relatively recently. We found there was a geographical distribution of resistance mutations, and relatively low rate of gene flow between populations, which has implications for the development and management of anticoagulant resistance.

Genetic tracking of mice and other bioproxies to infer human history

The long-distance movements made by humans through history are quickly erased by time but can be reconstructed by studying the genetic make-up of organisms that travelled with them. The phylogeography of the western house mouse (Mus musculus domesticus), whose current widespread distribution around the world has been caused directly by the movements of (primarily) European people, has proved particularly informative in a series of recent studies. The geographic distributions of genetic lineages in this commensal have been linked to the Iron Age movements within the Mediterranean region and Western Europe, the extensive maritime activities of the Vikings in the 9th to 11th centuries, and the colonisation of distant landmasses and islands by the Western European nations starting in the 15th century. We review here recent insights into human history based on phylogeographic studies of mice and other species that have travelled with humans, and discuss how emerging genomic methodologies will increase the precision of these inferences.

Transcriptome sequencing of black grouse (Tetrao tetrix) for immune gene discovery and microsatellite development

The black grouse (Tetrao tetrix) is a galliform bird species that is important for both ecological studies and conservation genetics. Here, we report the sequencing of the spleen transcriptome of black grouse using 454 GS FLX Titanium sequencing. We performed a large-scale gene discovery analysis with a focus on genes that might be related to fitness in this species and also identified a large set of microsatellites. In total, we obtained 182 179 quality-filtered sequencing reads that we assembled into 9035 contigs. Using these contigs and 15 794 length-filtered (greater than 200 bp) singletons, we identified 7762 transcripts that appear to be homologues of chicken genes. A specific BLAST search with an emphasis on immune genes found 308 homologous chicken genes that have immune function, including ten major histocompatibility complex-related genes located on chicken chromosome 16. We also identified 1300 expressed sequence tag microsatellites and were able to design suitable flanking primers for 526 of these. A preliminary test of the polymorphism of the microsatellites found 10 polymorphic microsatellites of the 102 tested. Genomic resources generated in this study should greatly benefit future ecological, evolutionary and conservation genetic studies on this species.

Fellow travellers: a concordance of colonization patterns between mice and men in the North Atlantic region

Background

House mice (Mus musculus) are commensals of humans and therefore their phylogeography can reflect human colonization and settlement patterns. Previous studies have linked the distribution of house mouse mitochondrial (mt) DNA clades to areas formerly occupied by the Norwegian Vikings in Norway and the British Isles. Norwegian Viking activity also extended further westwards in the North Atlantic with the settlement of Iceland, short-lived colonies in Greenland and a fleeting colony in Newfoundland in 1000 AD. Here we investigate whether house mouse mtDNA sequences reflect human history in these other regions as well.

Results

House mice samples from Iceland, whether from archaeological Viking Age material or from modern-day specimens, had an identical mtDNA haplotype to the clade previously linked with Norwegian Vikings. From mtDNA and microsatellite data, the modern-day Icelandic mice also share the low genetic diversity shown by their human hosts on Iceland. Viking Age mice from Greenland had an mtDNA haplotype deriving from the Icelandic haplotype, but the modern-day Greenlandic mice belong to an entirely different mtDNA clade. We found no genetic association between modern Newfoundland mice and the Icelandic/ancient Greenlandic mice (no ancient Newfoundland mice were available). The modern day Icelandic and Newfoundland mice belong to the subspecies M. m. domesticus, the Greenlandic mice to M. m. musculus.

Conclusions

In the North Atlantic region, human settlement history over a thousand years is reflected remarkably by the mtDNA phylogeny of house mice. In Iceland, the mtDNA data show the arrival and continuity of the house mouse population to the present day, while in Greenland the data suggest the arrival, subsequent extinction and recolonization of house mice - in both places mirroring the history of the European human host populations. If house mice arrived in Newfoundland with the Viking settlers at all, then, like the humans, their presence was also fleeting and left no genetic trace. The continuity of mtDNA haplotype in Iceland over 1000 years illustrates that mtDNA can retain the signature of the ancestral house mouse founders. We also show that, in terms of genetic variability, house mouse populations may also track their host human populations.

Norwegian house mice (Mus musculus musculus/domesticus): distributions, routes of colonization and patterns of hybridization

We investigated the distributions and routes of colonization of two commensal subspecies of house mouse in Norway: Mus musculus domesticus and M. m. musculus. Five nuclear markers (Abpa, D11 cenB2, Btk, SMCY and Zfy2) and a morphological feature (tail length) were used to differentiate the two subspecies and assess their distributions, and mitochondrial (mt) D-loop sequences helped to elucidate their colonization history. M. m. domesticus is the more widespread of the two subspecies, occupying the western and southern coast of Norway, while M. m. musculus is found along Norway's southeastern coast and east from there to Sweden. Two sections of the hybrid zone between the two subspecies were localized in Norway. However, hybrid forms also occur well away from that hybrid zone, the most prevalent of which are mice with a M. m. musculus-type Y chromosome and an otherwise M. m. domesticus genome. MtDNA D-loop sequences of the mice revealed a complex phylogeography within M. m. domesticus, reflecting passive human transport to Norway, probably during the Viking period. M. m. musculus may have colonized earlier. If so, that leaves open the possibility that M. m. domesticus replaced M. m. musculus from much of Norway, with the widely distributed hybrids a relict of this process. Overall, the effects of hybridization are evident in house mice throughout Norway.

Colonization, mouse-style

Several recent papers, including one in BMC Evolutionary Biology, examine the colonization history of house mice. As well as background for the analysis of mouse adaptation, such studies offer a perspective on the history of movements of the humans that accidentally transported the mice.

See research article: http://www.biomedcentral.com/1471-2148/10/325

Of mice and (Viking?) men: phylogeography of British and Irish house mice

The west European subspecies of house mouse (Mus musculus domesticus) has gained much of its current widespread distribution through commensalism with humans. This means that the phylogeography of M. m. domesticus should reflect patterns of human movements. We studied restriction fragment length polymorphism (RFLP) and DNA sequence variations in mouse mitochondrial (mt) DNA throughout the British Isles (328 mice from 105 localities, including previously published data). There is a major mtDNA lineage revealed by both RFLP and sequence analyses, which is restricted to the northern and western peripheries of the British Isles, and also occurs in Norway. This distribution of the 'Orkney' lineage fits well with the sphere of influence of the Norwegian Vikings and was probably generated through inadvertent transport by them. To form viable populations, house mice would have required large human settlements such as the Norwegian Vikings founded. The other parts of the British Isles (essentially most of mainland Britain) are characterized by house mice with different mtDNA sequences, some of which are also found in Germany, and which probably reflect both Iron Age movements of people and mice and earlier development of large human settlements. MtDNA studies on house mice have the potential to reveal novel aspects of human history.

The diverse origins of New Zealand house mice

Molecular markers and morphological characters can help infer the colonization history of organisms. A combination of mitochondrial (mt) D-loop DNA sequences, nuclear DNA data, external measurements and skull characteristics shows that house mice (Mus musculus) in New Zealand and its outlying islands are descended from very diverse sources. The predominant genome is Mus musculus domesticus (from western Europe), but Mus musculus musculus (from central Europe) and Mus musculus castaneus (from southern Asia) are also represented genetically. These subspecies have hybridized to produce combinations of musculus and domesticus nuclear DNA coupled with domesticus mtDNA, and castaneus or musculus mtDNA with domesticus nuclear DNA. The majority of the mice with domesticus mtDNA that we sampled had D-loop sequences identical to two haplotypes common in Britain. This is consistent with long-term British-New Zealand cultural linkages. The origins of the castaneus mtDNA sequences widespread in New Zealand are less easy to identify.

Mhc class I and non-class I gene organization in the proximal H2-M region of the mouse

A bacterial artificial chromosome (BAC) contig was constructed across the proximal part of the H2-M region from the major histocompatibility complex (Mhc) of mouse strain 129 (H2bc). The contig is composed of 28 clones that span approximately 1 megabasepair (Mb), from H2-T1 to Mog, and contains three H2-T genes and 18 H2-M genes. We report the fine mapping of the H2-M class I gene cluster, which includes the previously reported M4-M6, the M1 family, the M10 family, and four additional class I genes. All but two of the H2-M class I genes are conserved among haplotypes H2k, H2b, and H2bc, and only two genes are found in polymorphic HindIII fragments. Six evolutionarily conserved non-class I genes were mapped to a 180 kilobase interval in the distal part of the class I region in mouse, and their order Znf173-Rfb30-Tctex5-Tctex6- Tctex4-Mog was found conserved between human and mouse. In this Znf173-Mog interval, three mouse class I genes, M6, M4, and M5, which are conserved among haplotypes, occupy the same map position as the human HLA-A class I cluster, which varies among haplotypes and is diverged in sequence from the mouse genes. These results further support the view that class I gene diverge and evolve independently between species.

The mouse major histocompatibility complex: some assembly required

We have assembled a contig of 81 yeast artificial chromosome clones that spans 8 Mb and contains the entire major histocompatibility complex (Mhc) from mouse strain C57BL/6 (H2b), and we are in the process of assembling an Mhc contig of bacterial artificial chromosome (BAC) clones from strain 129 (H2bc), which differs from C57BL/6 in the H2-Q and H2-T regions. The current BAC contig extends from Tapasin to D17Leh89 with gaps in the class II, H2-Q, and distal H2-M regions. Only four BAC clones were required to link the class I genes of the H2-Q and H2-T regions, and no new class I gene was found in the previous gap. The proximal 1 Mb of the H2-M region has been analyzed in detail and is ready for sequencing; it includes 21 class I genes or fragments, at least 14 olfactory receptor-like genes, and a number of non-class I genes that clearly establish a conserved synteny with the class I regions of the human and rat Mhc.

BAC/YAC contigs from the H2-M region of mouse Chr 17 define gene order as Znf173-Tctex5-mog-D17Tu42-M3-M2

A yeast artificial chromosome (YAC) contig from the C57BL/6 (H2(b)) mouse was created from the major histocompatibility complex (Mhc, H2 in mouse) class Ib subregion, H2-M. It spans approximately 1.2 megabase (Mb) pairs and unites the previous >1.5-Mb YAC contigs (Jones et al. 1995) into a single contig, which includes 21 Mhc class I genes distal to H2-T1. A bacterial artificial chromosome (BAC) contig from the 129 (H2(bc)) mouse, spanning approximately 600 kilobases, was also built from Znf173 (Afp, a gene for acid finger protein), through Tctex5 (t-complex testis expressed-5) and Mog (myelin oligodendrocyte glycoprotein), to H2-M2. Twenty-four sequence-tagged site (STS) markers were newly developed, and 35 markers were mapped in the YAC/BAC contigs, which define the marker order as Cen - Znf173 - Tctex5 - Mog - D17Tu42 - D17Mit232 - H2-M3 - D17Leh525 - H2-M2 - Tel. The gene order of Znf173 - Tctex5 - Mog - D17Tu42 is conserved between mouse and human, showing that the middle H2-M region corresponds to the subregion of the human Mhc surrounding HLA-A.

Characterization of two class I genes from the H2-M region: evidence for a new subfamily

We cloned, sequenced, and mapped two divergent major histocompatibility class Ib genes from BALB/c mice. M9d and M10d both have the potential to encode full-length class I molecules, but transcripts were not readily detectable. M9 is 86% similar to M1 in its nucleotide sequence and maps next to it on YAC clones. M9 is only 64% similar to M10 and 60% to H2-K k. Probes from M10 define a new subfamily of eight class I genes in C3H mice; five cluster directly distal to H2-T1, and three are located between M9-1-7-8 and M6-4-5 in the H2-M region.

Mitochondrial DNA rearrangements associated with mF plasmid integration and plasmodial longevity in Physarum polycephalum

Plasmodial cultures of Physarum polycephalum have defined life spans and undergo a reproducible decline (senescence) before losing the ability to be subcultured. Studies of the mtDNA of a long-lived Physarum strain, which does not undergo senescence, revealed a 7. 9-kb insertion in its mtDNA. This insertion is derived from a mitochondrial plasmid which enhances mitochondrial fusion and mtDNA recombination. Four different recombination events are required to convert the parental mtDNA to the form found in the long-lived strain. An additional recombination event, which deletes a 2.4-kb region of the insert from the long-lived strain, has been identified in the mtDNA of a normally senescing strain. These observations imply a mitochondrial involvement in the process of plasmodial senescence and implicate a region of the DNA derived from the mitochondrial plasmid as being necessary for plasmodial longevity.

BAC clones and STS markers near the distal breakpoint of the fourth t-inversion, In(17)4d, in the H2-M region on mouse chromosome 17

The H2-M region is the most distal part of the mouse major histocompatibility complex (Mhc) and is likely to include the distal breakpoint of the fourth t-inversion, In(17)4d. The conserved synteny breakpoint between mouse and human is located in the H2-M region between D17Leh89, a putative olfactory receptor gene, and Pgk2 (phosphoglycerate kinase 2). To analyze the H2-M region, we screened a mouse bacterial artificial chromosome (BAC) library, using the D17Mit64, D17Tu49, D17Leh89, D17Leh467, and Pgk2 markers. Thirty-eight BAC clones were obtained and mapped in five clusters, and 25 sequence-tagged site (STS) markers were newly developed. The regions surrounding D17Tu49 and D17Leh467 are abundant in L1 repeat sequences and may, therefore, be candidates for the breakpoints of conserved synteny and t-inversion. D17Leh89 was linked to D17Mit64 by two contiguous BAC clones. The Aeg1 (acidic epididymal glycoprotein 1) and Aeg2 genes were mapped close to Pgk2, on the same BAC clones. The genetic length between D17Leh89-D17Mit64 and Pgk2-Aeg can be estimated as 0.5-0.7 centiMorgan (cM), and the most distal class I gene, H2-M2, can be placed 0.3-1.0 cM proximal to the t-inversion breakpoint. A recombinational hotspot is suggested to be located between Aeg and Tpxl in an interspecific cross of (C57BL/6J x Mus spretus).

Genomic evolution of the distal Mhc class I region on mouse Chr 17

A 5-Mb YAC contig, partly supplemented with BAC contigs, was created from the distal Mhc class I region on mouse Chr 17. The gene order of Znf173-Tctex5-Mog-D17Tu42-D17Leh 89 is conserved between mouse and human but not the physical distance, supporting the independent expansion of Mhc class I genes in the so-called accordion model of Mhc evolution. The distal H2-M region includes the breakpoint of conserved synteny between mouse and human as well as the In(17)4 t-inversion. The H2-M region is rich in L1 repeats, implying that the insertion of L1 repeats may be associated with the evolutionary flexibility to break a chromosome.

H2-M3, a full-service class Ib histocompatibility antigen

H2-M3 is an MHC class Ib molecule of the mouse with a unique preference for N-formylated peptides, which may come from the N-termini of endogenous, mitochondrial proteins or foreign, bacterial proteins. The crystal structure of M3 revealed a hydrophobic peptide-binding groove with an occluded A pocket and the peptide shifted one residue relative to class Ia structures. The formyl group is held by a novel hydrogen bonding network, involving His9 on the bottom of the groove, and the side chain of the P1 methionine is lodged in the B pocket. M3 is a full-service histocompatibility (H) antigen, i.e. self-M3 can present endogenous peptides as minor H antigens and foreign, bacterial antigens in a defensive immune response to infection; and foreign M3 complexed with endogenous self-peptides.

Physical mapping of the human and mouse MOG gene at the distal end of the MHC class Ib region

Myelin/oligodendrocyte glycoprotein (MOG) is expressed specifically in the central nervous system (CNS) by myelinating glial cells, the oligodendrocytes. The external location of MOG on myelin sheaths and its late expression during myelinogenesis argue for a role of MOG in the completion of myelin and maintenance of its integrity. MOG is a target autoantigen in demyelinating diseases, such as experimental autoimmune encephalomyelitis (EAE) in animals and multiple sclerosis (MS) in humans. We previously located the gene encoding MOG to the major histocompatibility complex (MHC), both in human, by cytogenetics, and in mouse, by analysis of recombinants. To refine the position, we have now selected yeast artificial chromosome clones (YAC) which contain the MOG gene. Physical mapping of the human MOG and the mouse Mog genes by characterization of these YAC clones indicated that the gene is located at the distal end of the major histocompatibility complex (MHC) class Ib region in both species. The human MOG gene lies 60 kilobases (kb) telomeric to HLA-F in a head-to-head orientation; the mouse Mog gene lies 25 (kb) telomeric to H2-M5 in a tail-to-head orientation. These orthologous genes provide markers for comparative analysis of the evolution of the MHC in the two species. The physical mapping of MOG should facilitate analysis of its role in hereditary neurological diseases, and the YAC clones identified here will permit the identification of new genes in the region.

MHC class I gene organization in > 1.5-Mb YAC contigs from the H2-M region

Sixteen yeast artificial chromosome (YAC) clones have been mapped to the H2-M region at the distal end of the mouse major histocompatibility complex (MHC) on chromosome 17. Analysis of the YACs with single- and multicopy probes yielded a proximal contig spanning a minimum of 800 kb and a distal contig of 700 kb. A probe for the conserved fourth exon of MHC class I genes detected 19 restriction fragments, including 6 of the 8 previously characterized H2-M class I genes, in the proximal contig. This contig spans the gap from the M to the T region and includes the T1 gene. By contrast, only two class I genes, M2 and M3, were found in the distal contig. These two genes, which are both expressed, may mark the end of the MHC. The order among nine class I genes and seven other markers was determined in the cloned DNA from the centromere as T1, Tu32A, (M1-M7-M8), Tu32B, B30, M6, M4, M5, Mog, Tu42A parallel M2, Leh525, M3, Tu42B, where the orientation with respect to the centromere is unknown for M1-M7-M8.

Mitochondrial DNA of Physarum polycephalum: physical mapping, cloning and transcription mapping

Mitochondrial DNA (mtDNA) has been isolated from four strains of Physarum polycephalum and a restriction site map has been determined using nine restriction enzymes. The restriction site maps of the four strains are similar but each strain is distinguished by insertions, deletions and restriction enzyme site polymorphisms. The sum of the restriction fragments gives mitochondrial genome sizes which vary from about 56 kb to 62 kb. In all four strains the composite map of the restriction enzyme sites for the mtDNA is circular. Knowledge of the restriction enzyme map has enabled cloning of mtDNA fragments representing the entire mtDNA of strain M3. The cloned fragments have been used to create a transcription map of the mtDNA.

Giant hepatic hemangiomas: diagnostic and therapeutic dilemmas

This report describes four cases of surgically treated giant hepatic hemangiomas which illustrate some diagnostic and therapeutic difficulties encountered in the management of this condition. An important diagnostic triad has emerged, which should alert the physician to the possibility of a complicated hepatic hemangioma: the clinical signs of an acute inflammatory liver process contrasted with a normal white blood cell count and liver function tests. Hemangiomas of the left lobe were either missed or poorly demonstrated on selective hepatic angiographic examination, and in two patients the diagnosis was made only at the time of laparotomy. Hepatic resection was successfully performed in all patients; there was minimal morbidity and none of the patients died. In two patients with multiple hemangiomas, only symptomatic or easily resectable lesions were removed. All patients are alive and well; three have been followed up for more than 5 years. We conclude that resection in asymptomatic cases should be carried out only in those cases that require a diagnostic laparotomy and in those where the lesion is easily resectable. The majority of patients with symptomatic and complicated tumors should undergo resection, but even in these patients continued conservative treatment is appropriate when the risk of major resection outweighs the small risk of live-threatening bleeding.

Allogeneic bone marrow transplantation: the monitoring of granulocyte macrophage colonies following the collection of bone marrow mononuclear cells and after the subsequent in-vitro cytolysis of OKT3 positive lymphocytes

Marrow nucleated cells from eight normal allogeneic donors was layered on Ficoll-Metrizoate to isolate the mononuclear cell fraction. The cells were then washed to remove Ficoll-Metrizoate and coagulation factors prior to resuspension in a balanced salt solution and the addition of the murine anti-human T-lymphocyte monoclonal antibody OKT3 and rabbit complement. The procedures were assessed for their effect on mononuclear cell viability (mean recovery 84.4%); the ability of the cells to proliferate granulocyte-macrophage colonies (mean recovery 57.4%); the in-vitro T-lymphocytolysis (mean 75.7%) and the removal of rabbit complement (greater than 99%). Following marrow transplantation with this treated mononuclear fraction the mean day to recovery of greater than or equal to 1.0 X 10(9)/l leucocytes was 20 d, with three patients developing greater than or equal to Grade II acute graft versus host disease (GvHD). Thus, treatment of donor marrow with OKT3 and complement in a large volume system was not detrimental to subsequent engraftment, nor effective in complete T-lymphocytolysis, nor in prevention of severe GvHD.