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M Nickells

Publications and source records attributed to M Nickells.

6 recordsLinked to original sources
PubMed2001

Neuroadapted yellow fever virus 17D: genetic and biological characterization of a highly mouse-neurovirulent virus and its infectious molecular clone.

A neuroadapted strain of yellow fever virus (YFV) 17D derived from a multiply mouse brain-passaged virus (Porterfield YF17D) was additionally passaged in SCID and normal mice. The virulence properties of this virus (SPYF) could be distinguished from nonneuroadapted virus (YF5.2iv, 17D infectious clone) by decreased average survival time in SCID mice after peripheral inoculation, decreased average survival time in normal adult mice after intracerebral inoculation, and occurrence of neuroinvasiveness in normal mice. SPYF exhibited more efficient growth in peripheral tissues of SCID mice than YF5.2iv, resulting in a more rapid accumulation of virus burden, but with low-titer viremia, at the time of fatal encephalitis. In cell culture, SPYF was less efficient in replication than YF5.2iv in all cell lines tested. The complete nucleotide sequence of SPYF revealed 29 nucleotide substitutions relative to YF5.2iv, and these were distributed throughout the genome. There were a total of 13 predicted amino acid substitutions, some of which correspond to known differences among the Asibi, French viscerotropic virus, French neurotropic vaccine, and YF17D vaccine strains. The envelope (E) protein contained five substitutions, within all three functional domains. Substitutions were also present in regions encoding the NS1, NS2A, NS4A, and NS5 proteins and in the 3' untranslated region (UTR). Construction of YFV harboring all of the identified coding nucleotide substitutions and those in the 3' UTR yielded a virus whose cell culture and pathogenic properties, particularly neurovirulence and neuroinvasiveness for SCID mice, generally resembled those of the original SPYF isolate. These findings implicate the E protein and possibly other regions of the genome as virulence determinants during pathogenesis of neuroadapted YF17D virus in mice. The determinants affect replication efficiency in both neural and extraneural tissues of the mouse and confer some limited host-range differences in cultured cells of nonmurine origin.

Animals↗
PubMed1998

Mapping epitopes for 20 monoclonal antibodies to CR1.

Complement receptor type one (CR1; CD35) binds and processes C3b and C4b opsonized immune complexes and regulates complement activation. We have characterized the epitopes of 13 previously reported and seven new MoAbs to human CR1. The MoAbs formed seven groups based on their reactivity with a panel of deletion forms of CR1. Seventeen of the MoAbs reacted with CR1 at more than one site, a consequence of its repetitive sequence. All five of the MoAbs recognizing epitopes in the nearly identical repeats 3, 10, and 17, as well as one MoAb which reacted with repeats 8 or 1/2 of 9 and 15 or 1/2 of 16, blocked cofactor activity for C3b. Knowledge of the repeats bearing the epitopes for these MoAbs should facilitate the further characterization of CR1.

Animals↗
PubMed1997

Primary sequence of baboon CR1 demonstrates concerted evolution within the CR1 gene.

Complement receptor type one (CR1) in primates has several remarkable structural features including a size polymorphism (Mr 190000, 220000, 250000 and 280000) in man, multiple size variants (Mr 55000-220000) among non-human primates, and a partial amino-terminal duplication (CR1-like gene) that appears to encode the short (55000-70000) forms expressed on primate erythrocytes. In general, these short CR1 forms, some of which are GPI anchored, are expressed on erythrocytes and the 220000 molecular weight CR1 form is expressed on PBMC, except in man, where only the 220000 molecular weight form has been detected. In addition, the Mr 220000 human CR1 sequence carries several long internal repeats of up to 99% homology. It has been suggested that the highest homology is maintained by gene conversion and/or unequal crossover. To address further the evolutionary and biologic implications of these multiple forms, a 6 kb cDNA encoding baboon CR1(220) was identified by RTPCR using human CR1 primers. Its sequence contains the expected 30 complement control protein repeats (CCP) and demonstrates an overall homology to human CR1 of 95.4% at the nucleotide level and 93.2% at the amino acid level. As in human CR1, the first 28 CCP maintain the characteristic "seven CCP-long homologous repeats (LHR)" organization. Analysis of baboon CR1(220) indicates that horizontal or concerted evolution has maintained a high degree (> 98%) of identity between corresponding CCP within the LHRs from CCP 4 to CCP 19, while this homology region extends from CCP 3 to CCP 18 in man. In contrast, substitutions occurring in other CCP are not propagated to the corresponding sites of other LHR. Sequence differences in CCP 1, 2 and 3 are likely to be related to the acquisition of enhanced C3b binding capability by this amino-terminal region of the protein. Thus, the sequence data strongly support the hypotheses that gene conversion and or unequal crossover events have driven the evolution of the protein in regions of high homology while selective forces, probably ligand binding requirements, have maintained the regions of divergence.

Amino Acid Sequence↗
PubMed1992

Identification and characterization of membrane cofactor protein of human spermatozoa.

Membrane cofactor protein (MCP) regulates C activation by serving as a cofactor for the cleavage of C3b and C4b by the serine protease factor I. An MCP-like molecule on the inner acrosomal membrane of human spermatozoa has been characterized. Three mAb and a rabbit polyclonal antibody against MCP recognized the sperm protein. On SDS-PAGE, it migrated as a single band with a molecular mass of 38,000 and 44,000 Da under nonreducing or reducing conditions, respectively. The molecular mass was 10,000 to 20,000 Da less than the two forms of MCP expressed on others cells. The electrophoretic pattern, by one- and two-dimensional gel analysis, and the isoelectric point profile (4.5 to 5.0) of the sperm protein were similar among multiple individuals. In contrast to MCP of other cells, digestion with endoglycosidases did not alter either the m.w. or the pI of the protein, suggesting that it is a poorly or nonglycosylated form of MCP. The solubilized sperm protein bound C3 with broken thioester bond to Sepharose and possessed cofactor activity for factor I-mediated cleavage of C3 with the broken bond. A mAb that blocks the regulatory function of MCP inhibited the cofactor activity of the sperm lysate. Thus, the sperm protein is an antigenic and functional homologue of MCP but has the distinct structural features of a lower m.w. and an apparent lack of glycosylation. MCP may play an essential role in the survival of the acrosome-reacted spermatozoa by modulating C activation in the female genital tract.

Acrosome↗
PubMed1987

Additional forms of human decay-accelerating factor (DAF).

Decay-accelerating factor (DAF) of human erythrocytes is a glycoprotein with a Mr of 65,000 that is anchored in the membrane via a glycolipid tail. During the purification of DAF, two lower m.w. forms were noted. DAF-A had an Mr of 63,000, and DAF-B had an Mr of 55,000. In a fluid phase assay, both forms accelerated the decay of the classical and the alternative C3 convertases with a specific activity similar to that of DAF. However, the decay-accelerating activity for the cell-bound C3 convertases was abolished, suggesting that neither could insert into E membranes and therefore that the glycolipid tail is altered. Analysis by molecular sieve high-pressure liquid chromatography demonstrated that DAF-A eluted with a Mr of approximately 450,000, similar to native DAF, and was thus in an aggregated form. In contrast, DAF-B eluted as a monomer with a Mr of approximately 60,000. DAF-A, but not DAF-B, bound to a hydrophobic column. To further characterize these two forms, surface-labeled human erythrocytes were incubated with phosphatidyl inositol-specific phospholipase C or papain. The phospholipase inefficiently released a form of DAF that was slightly larger (Mr of 64,000) than DAF-A. Papain efficiently released a 55,000 fragment that had the same Mr as DAF-B. To determine if DAF was cleaved by endogenous enzymes, surface-labeled erythrocytes were incubated with leukocytes. The kinetics of the leukocyte-induced degradation was similar to those observed with papain, and the released fragment aligned on seizing gels with the papain-derived fragment. We hypothesize that endogenous phospholipases and proteases cleave DAF to produce fragments similar to DAF-A and DAF-B, respectively.

Butanols↗