Biomedical subjects

Daudi K Langat

Publications and source records attributed to Daudi K Langat.

9 recordsLinked to original sources

PubMed2006

Differential expression of human leukocyte antigen-G (HLA-G) messenger RNAs and proteins in normal human prostate and prostatic adenocarcinoma.

Human leukocyte antigen-G (HLA-G) is a major histocompatibility complex class Ib gene expressed in normal organs and in some tumors. The glycoproteins encoded by this gene are best known for their immunosuppressive properties. Because isoform-specific expression of HLA-G in male reproductive organs has not been reported, we investigated HLA-G1, -G2, -G5, -G6 mRNAs and proteins in four-to-five samples of normal prostate glands, prostates with benign prostatic hyperplasia and prostate adenocarcinomas using RT-PCR and immunohistochemistry. All tissues contained HLA-G1, -G2, -G5 and -G6 specific mRNAs, but only HLA-G5 protein was detectable. In normal prostate glands, HLA-G5 protein was prominent in the cytoplasm of tubuloglandular epithelia and in glandular secretions. Staining was reduced in samples of benign prostatic hyperplasia but remained localized to the cytoplasm of glandular epithelia and secretions. In prostatic adenocarcinomas, HLA-G5 protein was detectable mainly in the secretions. Thus, HLA-G5 but not HLA-G1, -G2 or -G6 is produced in the normal prostate and is present in prostatic secretions. In addition, normal cellular localization is disturbed in benign and malignant prostatic adenocarcinomas. The results are consistent with this molecule may influencing female immune receptivity to sperm and suggest that such immunosuppression could be disturbed in men with prostatic adenocarcinomas.

Adenocarcinoma↗

PubMed2006

The role of HLA-G in human pregnancy.

Pregnancy in mammals featuring hemochorial placentation introduces a major conflict with the mother's immune system, which is dedicated to repelling invaders bearing foreign DNA and RNA. Numerous and highly sophisticated strategies for preventing mothers from rejecting their genetically different fetus(es) have now been identified. These involve production of novel soluble and membrane-bound molecules by uterine and placental cells. In humans, the placenta-derived molecules include glycoproteins derived from the HLA class Ib gene, HLA-G. Isoforms of HLA-G saturate the maternal-fetal interface and circulate in mothers throughout pregnancy. Uteroplacental immune privilege for the fetus and its associated tissues is believed to result when immune cells encounter HLA-G. Unequivocally demonstration of this concept requires experiments in animal models. Both the monkey and the baboon express molecules that are similar but not identical to HLA-G, and may comprise suitable animal models for establishing a central role for these proteins in pregnancy.

Animals↗

PubMed2006

Methods for evaluating histocompatibility antigen gene expression in the baboon.

A wide variety of techniques has been developed for qualitative and quantitative analysis of gene expression in human cells and tissues. Two commonly used methods are reverse-transcription (RT)-polymerase chain reaction (PCR) to analyze the transcribed messenger RNAs (mRNA) and immunohistochemistry to detect the translated proteins. These techniques can be modified and adapted for use in analyzing gene expression in animal models. In particular, as a result of the close phylogenetic relationship between humans and nonhuman primates, human reagents, especially antibodies, cross-react with nonhuman primate tissues. However, the results are not always satisfactory as some antibodies may cross-react with irrelevant antigens in these tissues. In this chapter, we describe the use of RT-PCR and immunohistochemical techniques to analyze expression of Paan-AG, a novel class lb major histocompatibility complex antigen in the olive baboon (Papio anubis) placenta. We used Paan-AG-specific primers to amplify Paan-AG transcripts from baboon placenta, and generated Paan-AG isoform-specific polyclonal antibodies for use in immunohistochemistry.

Animals↗

PubMed2005

Widely varying SIV prevalence rates in naturally infected primate species from Cameroon.

Although it is now well established that a substantial proportion of wild-living primates in sub-Saharan Africa harbor SIV, no study to date has examined to what extent the various species are naturally infected. In this study, we first describe the development and validation of sensitive and specific SIV antibody detection assays representing all major known primate lentiviral lineages on a panel of 207 sera from 11 different primate species with known infection status. The newly developed assays were then used to determine SIV prevalence rates in nine primate species native to Cameroon. Analysis of 722 sera revealed widely varying prevalence rates, ranging from an apparent absence of SIV infection in crested mona (0/70), grey cheeked (0/36) and agile mangabeys (0/92), to prevalence rates of 3%, 4%, 11%, 27%, 39% and 52% for mustached (6/203), greater spot-nosed (8/193), northern talapoin (3/26), mantled guereza (14/52), De Brazza's (9/23) and mandrill (14/27) monkeys, respectively. The epidemiology of naturally occurring SIV infections is thus more complex than previously appreciated and the various non-human primate hosts seem to differ in their susceptibility to SIV infection. The newly developed assays should now permit to define with greater accuracy existing SIV reservoirs and associated human zoonotic risk.

Amino Acid Sequence↗

PubMed2005

Khat (Catha edulis) up-regulates testosterone and decreases prolactin and cortisol levels in the baboon.

The potential effect of Khat (Catha edulis, Celastraceae) on fertility in humans has not been elucidated. In this study, we used the olive baboon (Papio anubis, Cercopithecidae) to determine the effects of oral administration of khat on circulating hormones. In order to establish baseline hormonal levels, five male baboons were bled once a week for 1 month. The same baboons were then fed with crude khat juice extract once a week over a period of 2 months, and the effects on serum levels of cortisol, testosterone and prolactin determined using enzyme immunoassay (EIA) and radioimmunoassay (RIA). Subsequently, sampling was repeated for a further 1 month to determine the residual effect of khat. The results showed that khat administration causes a significant increase in the mean levels of testosterone while prolactin and cortisol levels were reduced. These effects were also evident 1 month post treatment and indicate khat may exert a transient effect on male fertility by interfering with the hormonal profiles.

Administration, Oral↗

PubMed2004

Potential regulatory sequences in the untranslated regions of the baboon MHC class Ib gene, Paan-AG, more closely resemble those in the human MHC class Ia genes than those in the class Ib gene, HLA-G.

The baboon major histocompatibility complex (MHC) class Ib gene, Paan-AG, is structurally similar to the human MHC class Ia gene, HLA-A, but exhibits characteristics similar to those of the class Ib gene HLA-G. These include limited polymorphism, alternative splicing of a single message, and restricted tissue distribution, with high expression in the placenta. In order to determine whether regulatory elements controlling expression of Paan-AG resemble those of HLA-A or HLA-G, we cloned the 5' and 3' untranslated regions of Paan-AG. Unexpectedly, sequence comparisons showed that potential regulatory elements in Paan-AG strikingly resembled those in HLA-A and differed in major respects from those in HLA-G. Unlike HLA-G, Paan-AG contained an intact interferon-gamma stimulated response element (ISRE) in the promoter. Studies using luciferase reporter assays showed that the Paan-AG ISRE was functional. The basal activity of the Paan-AG ISRE and its response to interferon-gamma was similar to that of class Ia MHC genes. Further, we identified an ISRE in the 3' untranslated region of Paan-AG that is known to be functional in HLA-A2 but is deleted in HLA-G. These experiments predict that functional studies may demonstrate differences in regulation of expression of Paan-AG and HLA-G genes, which could restrict the use of the baboon as a primate model for studying HLA-G expression and function.

Animals↗

PubMed2004

New simian immunodeficiency virus infecting De Brazza's monkeys (Cercopithecus neglectus): evidence for a cercopithecus monkey virus clade.

Nearly complete sequences of simian immunodeficiency viruses (SIVs) infecting 18 different nonhuman primate species in sub-Saharan Africa have now been reported; yet, our understanding of the origins, evolutionary history, and geographic distribution of these viruses still remains fragmentary. Here, we report the molecular characterization of a lentivirus (SIVdeb) naturally infecting De Brazza's monkeys (Cercopithecus neglectus). Complete SIVdeb genomes (9,158 and 9227 bp in length) were amplified from uncultured blood mononuclear cell DNA of two wild-caught De Brazza's monkeys from Cameroon. In addition, partial pol sequences (650 bp) were amplified from four offspring of De Brazza's monkeys originally caught in the wild in Uganda. Full-length (9068 bp) and partial pol (650 bp) SIVsyk sequences were also amplified from Sykes's monkeys (Cercopithecus albogularis) from Kenya. Analysis of these sequences identified a new SIV clade (SIVdeb), which differed from previously characterized SIVs at 40 to 50% of sites in Pol protein sequences. The viruses most closely related to SIVdeb were SIVsyk and members of the SIVgsn/SIVmus/SIVmon group of viruses infecting greater spot-nosed monkeys (Cercopithecus nictitans), mustached monkeys (Cercopithecus cephus), and mona monkeys (Cercopithecus mona), respectively. In phylogenetic trees of concatenated protein sequences, SIVdeb, SIVsyk, and SIVgsn/SIVmus/SIVmon clustered together, and this relationship was highly significant in all major coding regions. Members of this virus group also shared the same number of cysteine residues in their extracellular envelope glycoprotein and a high-affinity AIP1 binding site (YPD/SL) in their p6 Gag protein, as well as a unique transactivation response element in their viral long terminal repeat; however, SIVdeb and SIVsyk, unlike SIVgsn, SIVmon, and SIVmus, did not encode a vpu gene. These data indicate that De Brazza's monkeys are naturally infected with SIVdeb, that this infection is prevalent in different areas of the species' habitat, and that geographically diverse SIVdeb strains cluster in a single virus group. The consistent clustering of SIVdeb with SIVsyk and the SIVmon/SIVmus/SIVgsn group also suggests that these viruses have evolved from a common ancestor that likely infected a Cercopithecus host in the distant past. The vpu gene appears to have been acquired by a subset of these Cercopithecus viruses after the divergence of SIVdeb and SIVsyk.

Amino Acid Sequence↗

PubMed2002

Baboon placentas express soluble and membrane-bound Paan-AG proteins encoded by alternatively spliced transcripts of the class Ib major histocompatibility complex gene, Paan-AG.

The human class Ib major histocompatibility complex (MHC) molecule, HLA-G, is unique in its limited polymorphism, high expression in the placenta and generation of multiple transcripts by alternative splicing. The proteins encoded by these transcripts are believed to modulate maternal-fetal immunological relationships during pregnancy. The baboon placenta contains messages encoded by a novel MHC gene, Paan-AG, which is evolutionarily related to the HLA-A locus, but shares unique characteristics with HLA-G. In this study, we show that the Paan-AG message is alternatively spliced to generate at least seven transcripts. One of these transcripts retains intron 4 and encodes a soluble glycoprotein with three external domains and a unique 21-amino-acid sequence at the carboxyl terminus, similar to soluble HLA-G1. This glycoprotein was detected in first trimester placental villous cytotrophoblast and syncytiotrophoblast, and in extravillous cytotrophoblast cells in the basal plate in term placenta. Four of the transcripts ( Paan-AG1, Paan-AG2, Paan-AG3, Paan-AG4) encode membrane-bound class Ib MHC glycoprotein isoforms. Paan-AG1 protein expression was similar to that of sPaan-AG, while Paan-AG2 protein was not detected in these tissues. The other two transcripts ( Paan-AGx and Paan-AGxi) contain a truncated exon 3 and multiple stop codons. Paan-AG1 and Paan-AGx transcripts were detected in a number of non-placental tissues, but these transcripts contained multiple stop codons. Because of the structural similarities and common features of organ-specific expression and splicing of the message, studies on Paan-AG may be of value in dissecting the functions of the class Ib proteins in human pregnancy.

Alternative Splicing↗

PubMed2002

Do nonhuman primates comprise appropriate experimental models for studying the function of human leukocyte antigen-G?

The expression and function of the human major histocompatibility complex (MHC) class Ia genes, human leukocyte antigen (HLA)-A, -B, and -C, is well-established; they are expressed in most nucleated cells and present endogenous peptides to CD8+ T cells. However, MHC class Ib genes are poorly characterized and have unknown functions. In humans, the best-characterized class Ib gene is HLA-G. This gene has a restricted tissue expression of the mRNA and a unique pattern of protein expression; it is expressed mainly in the extravillous cytotrophoblast cells in the placenta. The function of HLA-G is not clear, but its presence at the maternal-fetal interface suggests a role in protection of the semiallogeneic fetus. Whereas functional studies using in vitro models and transgenic mice provide useful insights regarding the potential function of this molecule, in vivo studies cannot be performed in humans. Nonhuman primates that are closely related to humans phylogenetically contain homologues of HLA-G. The MHC-G loci in nonhuman primates appear to have diverged from the human HLA-G. However, in the rhesus monkey (Macaca mulatta) and olive baboon (Papio anubis), a novel class Ia-related locus has been described. This gene encodes glycoproteins with characteristics that resemble those of HLA-G, including restricted tissue distribution, alternative splicing of mRNA, truncated cytoplasmic domain, and limited polymorphism. Thus, this molecule may be the functional homologue of HLA-G, and these two species may comprise appropriate models for elucidating the function of HLA-G.

Animals↗