Regulators of complement activity mediate inhibitory mechanisms through a common C3b‐binding mode

Regulators of complement activation (RCA) inhibit complement‐induced immune responses on healthy host tissues. We present crystal structures of human RCA (MCP, DAF, and CR1) and a smallpox virus homolog (SPICE) bound to complement component C3b. Our structural data reveal that up to four consecutive homologous CCP domains (i–iv), responsible for inhibition, bind in the same orientation and extended arrangement at a shared binding platform on C3b. Large sequence variations in CCP domains explain the diverse C3b‐binding patterns, with limited or no contribution of some individual domains, while all regulators show extensive contacts with C3b for the domains at the third site. A variation of ~100° rotation around the longitudinal axis is observed for domains binding at the fourth site on C3b, without affecting the overall binding mode. The data suggest a common evolutionary origin for both inhibitory mechanisms, called decay acceleration and cofactor activity, with variable C3b binding through domains at sites ii, iii, and iv, and provide a framework for understanding RCA disease‐related mutations and immune evasion.     

Production and characterization of polyclonal and monoclonal antibodies against Aflatoxin B1 oxime-BSA in an enzyme-linked immunosorbent assay

From a single aflatoxin B₁ oxime — bovine serum albumin conjugate, polyclonal and monoclonal antibody preparations were produced. The four rabbit polyclonal antisera were specific for aflatoxin Bi in a microtitration plate enzyme — linked immunosorbent assay. The monoclonal antibodies showed a wide range of differing specificities, recognizing, for example, aflatoxins B₁, B₂, G₁ and G₂; B₁ and B₂; B₁ and G₁; and G₁ alone. No antibody preparations reacted with aflatoxin M₁. The significance of these results to the strategy of anti-aflatoxin antibody production for use in quantitative enzyme immunoassays is discussed.     

Preliminary evidence of genetic control of the immune response to the Thy-1.2 antigen in mice

The primary immune response to the Thy-1.2 antigen was measured by the plaque assay, detecting cells (PFC) producing antibodies lytic for thymocytes carrying this antigen. On the basis of statistically significant differences in response, the inbred strains studied could be classified as low (producing fewer than 10³ PFC/spleen) or high (producing more than 10³ PFC/spleen) responders. The data collected from these inbred strains and segregating generations were consistent with the concept that the primary immune response to the Thy-1.2 antigen is under genetic control. This control appeared to be exerted primarily by alleles at a locus linked to theH-2 complex but involvement of alleles at other loci could not be ruled out. Contrary to the commonly described experimental models, the high responsiveness to the Thy-1.2 antigen in some strain combinations seemed to be a recessive rather than a codominant trait.     

Immune response of mice to the Thy-1.1 antigen: Effect of theIr-5 alleles studied in 129/J and B10.129 (6M) mice

The primary immune response to the Thy-1.1 antigen was measured by a plaque assay that detected cells producing antibodies lytic for AKR thymocytes. B10.129(6M) mice carrying theH-2 complex of an intermediate responder (129) on a low-responder (B10) background, were low responders. Studies employing different F₁ hybrids and segregating generations of 129/J and 6M mice indicated that differences in responsiveness of those two strains depend on alleles at a single locus, loosely linked to theH-2 complex. These results lend further support to the previously advanced concept that the expression of theIr-Thy-1 allcles controlling the response to the Thy-1.1 antigen is influenced by the alleles at theIr-5 locus. In addition, studies employing F₁ hybrids produced through matings of 129/J, 6M, C3H.B10 and C57BL/6J mice to a panel of inbred strains suggested that in regard to the responsiveness to the Thy-1.1 antigen, 129/J and 6M mice are phenotypically, and presumably genotypically, similar to C3H.B10 and C57BL/6J mice, respectively.     

Immune response of mice to Thy-1.1 antigen: Studies on congenic lines

The primary response to Thy-1.1 antigen was measured by a plaque assay that detected cells producing antibodies lytic for AKR thymocytes (PFC). TheH-2 congenic mice (B10.K and B10.BR) carryingH-2 complexes of high responders (CBA and C57BR) on the low-responder background (B10) were found to produce significantly fewer PFC than the corresponding donor of theH-2 complex. On the other hand, C3H.B10 mice carrying theH-2 complex of a low responder on the high-responder background produced significantly more PFC than the donor of theH-2 complex. These findings were interpreted as evidence that alleles at previously described loci believed to be components of theI region of theH-2 complex and controlling immune response to Thy-1.1 are influenced by alleles at another locus. Studies of segregating populations of theH-2 congenic lines supplied evidence that this locus, tentatively calledIr-5, is in chromosome 17 (linkage group IX).     

The XXXXY Chromosome Anomaly: Report of Three New Cases and Review of 30 Cases from the Literature

The majority of abnormal sex chromosome complexes in the male have been considered to be variants of Klinefelter''s syndrome but an exception should probably be made in the case of the XXXXY individual who has distinctive phenotypic features. Clinical, radiological and cytological data on three new cases of XXXXY syndrome are presented and 30 cases from the literature are reviewed. In many cases the published clinical and radiological data were supplemented and re-evaluated. Mental retardation, usually severe, was present in all cases. Typical facies was observed in many; clinodactyly of the fifth finger was seen in nearly all.Radiological examination revealed abnormalities in the elbows and wrists in all the 19 personally evaluated cases, and other skeletal anomalies were very frequent. Cryptorchism is very common and absence of Leydig''s cells may differentiate the XXXXY chromosome anomaly from polysomic variants of Klinefelter''s syndrome. The relationship of this syndrome to Klinefelter''s syndrome and to Down''s syndrome is discussed.     

Differential responsiveness to immunoablative therapy in refractory rheumatoid arthritis is associated with level and avidity of anti-cyclic citrullinated protein autoantibodies: a case study

In order to identify pathogenic correlates of refractory rheumatoid arthritis (RA), antibodies against anti-cyclic citrullinated protein (ACPAs) were investigated in RA patients in whom the dysregulated immune system had been ablated by high-dose chemotherapy (HDC) and autologous haematopoietic stem cell transplantation (HSCT). Six patients with refractory RA were extensively characterized in terms of levels of total immunoglobulins, RA-specific autoantibodies (ACPAs and rheumatoid factor) and antibodies against rubella, tetanus toxoid (TT) and phosphorylcholine before and after HDC plus HSCT. Additionally, the avidity of ACPAs was measured before and after treatment and compared with the avidity of TT antibodies following repeated immunizations. Synovial biopsies were obtained by arthroscopy before HDC plus HSCT, and analyzed by immunohistochemistry. In the three patients with clinically long-lasting responses to HDC plus HSCT (median 423 days), significant reductions in ACPA-IgG levels after therapy were observed (median level dropped from 215 to 34 arbitrary units/ml; P = 0.05). In contrast, stable ACPA-IgG levels were observed in three patients who relapsed shortly after HDC plus HSCT (median of 67 days). Clinical responders had ACPA-IgG of lower avidity (r = 0.75; P = 0.08) and higher degree of inflammation histologically (r = 0.73; P = 0.09). Relapse (after 38 to 530 days) in all patients was preceded by rising levels of low avidity ACPA-IgG (after 30 to 388 days), in contrast to the stable titres of high avidity TT antibodies. In conclusion, humoral autoimmune responses were differentially modulated by immunoablative therapy in patients with synovial inflammation and low avidity ACPA-IgG autoantibodies as compared with patients with high levels of high avidity ACPA-IgG. The distinct clinical disease course after immunoablative therapy based on levels and avidity of ACPA-IgG indicates that refractory RA is not a single disease entity.     

The multiple sex chromosomes of platypus and echidna are not completely identical and several share homology with the avian Z

Background

Sex-determining systems have evolved independently in vertebrates. Placental mammals and marsupials have an XY system, birds have a ZW system. Reptiles and amphibians have different systems, including temperature-dependent sex determination, and XY and ZW systems that differ in origin from birds and placental mammals. Monotremes diverged early in mammalian evolution, just after the mammalian clade diverged from the sauropsid clade. Our previous studies showed that male platypus has five X and five Y chromosomes, no SRY, and DMRT1 on an X chromosome. In order to investigate monotreme sex chromosome evolution, we performed a comparative study of platypus and echidna by chromosome painting and comparative gene mapping.

Results

Chromosome painting reveals a meiotic chain of nine sex chromosomes in the male echidna and establishes their order in the chain. Two of those differ from those in the platypus, three of the platypus sex chromosomes differ from those of the echidna and the order of several chromosomes is rearranged. Comparative gene mapping shows that, in addition to bird autosome regions, regions of bird Z chromosomes are homologous to regions in four platypus X chromosomes, that is, X₁, X₂, X₃, X₅, and in chromosome Y₁.

Conclusion

Monotreme sex chromosomes are easiest to explain on the hypothesis that autosomes were added sequentially to the translocation chain, with the final additions after platypus and echidna divergence. Genome sequencing and contig anchoring show no homology yet between platypus and therian Xs; thus, monotremes have a unique XY sex chromosome system that shares some homology with the avian Z.