A transgenic marker expressed on discrete populations during B-cell development.

We describe a transgenic mouse strain that selectively express a surface marker (huCD25) on transitional B cells, pre-B cells and a lineage unidentified bone marrow (BM) population. We show that a subpopulation of B cells in Peyer's patches, spleen, blood and BM expressed the transgenic huCD25 marker on the cell surface. In the spleen, the huCD25 expression was found on transitional B cells, that had not yet been recruited into the recirculating pool. In the BM a fraction of the B220low surface immunoglobulin (Ig) negative PB493+ pre-B cells were huCD25+. HuCD25 expression was also seen on practically all immature B cells while the mature recirculating B cells did not express huCD25. A huCD25+B220- cell population was also found in the BM that had not rearranged the Ig heavy chain locus and did not express the lineage markers CD3, T-cell receptor (TCR), CD19 and Mac-1. A low expression of CD4 on these cells may indicate that they represent a noncommitted, hematopoetic progenitor cell population.

Joining chain-expressing and -nonexpressing B cell populations in the mouse.

The diphtheria toxin A chain (DTA) was gene targeted into the Joining chain (J chain) locus to create a mouse strain selecting against J chain-expressing cells, JDTA mice. Serum immunoglobulin (Ig)M and serum IgG were reduced six to eightfold, while serum IgA was elevated 14-fold in these mice. JDTA mice were immune competent although the serum Ig response compared with wild-type mice was reduced sixfold at day 14 but only fourfold at day 45 after immunization. Exchanging the DTA gene with a cDNA for c-myc resulted in mice with a distinct phenotype with increased Ig production and enhanced humoral immune responses. Analysis of single B cells stimulated by lipopolysaccharide in vitro using reverse transcription-polymerase chain reaction showed that J chain-nonexpressing B cells could be detected that had a secretory phenotype as determined by an abundance of transcript for secretory IgM. Finally, limiting dilution analysis of peripheral B cells showed that J chain expression was a clonal property already established in naive, peripheral B lymphocytes.

Complex genetic control in a rat model for rheumatoid arthritis.

We have defined previously five quantitative trait loci controlling development of pristane-induced arthritis in a cross between E3 and DA rats. To define new loci controlling the disease we have mapped three recombinant inbred strains between DA and E3 and analysed an F2 cross between DA rats and one of these RI strains. Two novel loci affecting disease severity are identified on chromosome 1 (Pia8) and chromosome 4 (Pia7) respectively. We could also reproduce the earlier identified Pia3 locus on chromosome 6 associated with arthritis onset. In the original E3xDA F2 cross, neither of the loci Pia7, Pia8, or Pia1 showed any association with arthritis. To investigate the possibility of interacting loci preventing the phenotypic expression of other loci, the E3xDA F2 cross was re-analysed with a model for a two locus interaction, knowing the presence of these newly identified loci. We found suggestive evidence for an interaction where an effect of Pia7 and Pia1 on disease severity depends on DA homozygosity at specific loci, which themselves do not confer susceptibility. This shows that additional disease associated loci can be identified if other loci are neutralized. This will be of importance for understanding the complex genetics controlling rheumatoid arthritis.

Genetic control of arthritis onset, severity and chronicity in a model for rheumatoid arthritis in rats.

Rheumatoid arthritis (RA) is a chronic and genetically complex inflammatory disorder that leads to erosive destruction of peripheral joints. The use of animal models mimicking RA, such as pristane-induced arthritis (PIA) in rats, should facilitate its genetic analysis. Pristane is a non-immunogenic synthetic oil that, after a single subcutaneous injection into DA rats, induces arthritis restricted to peripheral joints with a chronic relapsing disease course. To identify genes involved in the control of chronic arthritis, we made crosses between susceptible DA rats and resistant E3 rats and analysed the progeny with microsatellite markers covering the entire rat genome. Our results show that different arthritis phenotypes are associated with different chromosomal loci. Loci on chromosomes 4 and 6 (Pia2 and Pia3) influence arthritis onset, whereas a locus on chromosome 12 (Pia4) is associated with severity and joint erosion. We found that chronicity is associated with a different set of loci, one on chromosome 4 and the other on chromosome 14 (Pia5, Pia6). These findings demonstrate for the first time that different phases of a chronic self-perpetuative disease which mimics RA are associated with distinct sets of genes.

Increased serum levels of cartilage oligomeric matrix protein in chronic erosive arthritis in rats.

OBJECTIVE: To investigate the utility of serum cartilage oligomeric matrix protein (COMP) for disease monitoring in rats with chronic pristane-induced arthritis, and to examine the influence of age, sex, and genes on COMP concentrations in rat serum. METHODS: Serum COMP levels were quantified by immunoassay. Sera were obtained from DA, E3, and (E3 x DA)F1 rats each week between the ages of 4 and 30 weeks. The (E3 x DA)F2 (second generation after intercrossing) rats were injected intradermally with the synthetic oil pristane. Arthritis was monitored by a macroscopic scoring system, and serum levels of COMP were measured on days 6, 35, and 49 after immunization. RESULTS: Serum levels of COMP decreased during growth, and reached a plateau after the age of 12 weeks. The DA rats had higher COMP levels than the E3 rats, and the (E3 x DA)F1 rats had intermediate levels. No differences were observed in these levels when the rats were grouped by sex. Arthritic (E3 x DA)F2 rats had increased serum concentrations of COMP on days 35 and 49 after pristane injection (P < 0.0001 versus the nonarthritic animals). COMP levels correlated with the severity of macroscopically detectable arthritis at both time points (r > 0.9). Rats with a chronic disease course were distinguished by higher serum concentrations of COMP during the acute stage than animals with similar clinical scores but with resolving arthritis (P < 0.01). CONCLUSION: Serum analyses of COMP offer promise for monitoring tissue involvement in experimental arthritis. Such analyses should be useful for monitoring therapeutic interventions aimed at retarding tissue destruction as well as for studies of the genetically determined regulation of COMP turnover and susceptibility to arthritis. The application of molecular marker measurements to experimental arthritis offers a new possibility for verifying the utility of such measurements in human arthritis.