Preimplantation development of mouse embryos in KSOM: augmentation by amino acids and analysis of gene expression

Simplex optimization has generated several media that have improved the development of mouse preimplantation embryos in vitro. One objective of this study was to compare the development of preimplantation mouse embryos in one of these computer-optimized media, KSOM, with embryos that developed in vivo, in terms of the relative abundances of specific mRNAs involved in metabolism, transcription, and cell proliferation. First, however, since studies have indicated an improvement of other simple embryo culture media by addition of amino acids, the effects of the addition of amino acids to KSOM (KSOM/AA) on preimplantation development were assessed. We find that addition of both essential and nonessential amino acids to KSOM augments development in vitro, as compared to development supported by KSOM without amino acids. This augmentation is observed starting at the blastocyst stage, and is associated with increased rate of development to the blastocyst stage, increased frequency of hatching, and increased number of cells in the blastocysts. Reverse-transcription PCR was then used to assess the relative abundance of mRNAs for actin, glyceraldehyde-3-phosphate dehydrogenase, Na+, K(+)-ATPase, Sp1, TATA box-binding protein TBP, IGF-I, IGF-II, IGF-I receptor, and IGF-II receptor in embryos that developed in vivo and in vitro using KSOM/AA. Eight out of 9 of these mRNAs were present in the 8-cell embryos and blastocysts raised in KSOM/AA in amounts that were indistinguishable from those in embryos that developed in vivo. It is concluded that KSOM/AA provides an environment in which preimplantation mouse embryos can undergo development that is quantitatively similar to that occurring in vivo.

Case-control study of risk factors for avian influenza A (H5N1) disease, Hong Kong, 1997

In May 1997, a 3-year-old boy in Hong Kong died of a respiratory illness related to influenza A (H5N1) virus infection, the first known human case of disease from this virus. An additional 17 cases followed in November and December. A case-control study of 15 of these patients hospitalized for influenza A (H5N1) disease was conducted using controls matched by age, sex, and neighborhood to determine risk factors for disease. Exposure to live poultry (by visiting either a retail poultry stall or a market selling live poultry) in the week before illness began was significantly associated with H5N1 disease (64% of cases vs. 29% of controls, odds ratio, 4.5, P=.045). By contrast, travel, eating or preparing poultry products, recent exposure to persons with respiratory illness, including persons with known influenza A (H5N1) infection, were not associated with H5N1 disease.

Neisseria meningitidis porin PorB interacts with mitochondria and protects cells from apoptosis

Neisserial porins are strong immune adjuvants and B cell activators. The effect of neisserial porin PorB on activation-induced cell death was investigated, as a potential additional mechanism of the porin's immunopotentiating ability. Neisserial porins interact with target cells to localize intracellularly in the mitochondrial compartment without negatively affecting cellular survival. Pretreatment with Neisseria meningitidis PorB porin decreased or abrogated the mitochondrial damage induced by apoptotic stimuli. In addition, end stage determinants of apoptosis, including DNA breakdown, were diminished by PorB. Immunoprecipitation experiments revealed that PorB interacts with the mitochondrial porin VDAC (voltage-dependent anion channel). The mechanism of the antiapoptotic effect of neisserial porins could be explained by the protein-protein interaction of PorB with VDAC, similar to the interaction of VDAC with antiapoptotic Bcl-2 proteins, resulting in an enhancement of cell survival and continued activation of B cells.

An essential component of a C-terminal domain phosphatase that interacts with transcription factor IIF in Saccharomyces cerevisiae

One of the essential components of a phosphatase that specifically dephosphorylates the Saccharomyces cerevisiae RNA polymerase II (RPII) large subunit C-terminal domain (CTD) is a novel polypeptide encoded by an essential gene termed FCP1. The Fcp1 protein is localized to the nucleus, and it binds the largest subunit of the yeast general transcription factor IIF (Tfg1). In vitro, transcription factor IIF stimulates phosphatase activity in the presence of Fcp1 and a second complementing fraction. Two distinct regions of Fcp1 are capable of binding to Tfg1, but the C-terminal Tfg1 binding domain is dispensable for activity in vivo and in vitro. Sequence comparison reveals that residues 173-357 of Fcp1 correspond to an amino acid motif present in proteins of unknown function predicted in many organisms.

Role of the casein kinase I isoform, Hrr25, and the cell cycle-regulatory transcription factor, SBF, in the transcriptional response to DNA damage in Saccharomyces cerevisiae

In the budding yeast, Saccharomyces cerevisiae, DNA damage or ribonucleotide depletion causes the transcriptional induction of an array of genes with known or putative roles in DNA repair. The ATM-like kinase, Mec1, and the serine/threonine protein kinases, Rad53 and Dun1, are required for this transcriptional response. In this paper, we provide evidence suggesting that another kinase, Hrr25, is also involved in the transcriptional response to DNA damage through its interaction with the transcription factor, Swi6. The Swi6 protein interacts with Swi4 to form the SBF complex and with Mbp1 to form the MBF complex. SBF and MBF are required for the G1-specific expression of G1 cyclins and genes required for S-phase. We show that Swi6 associates with and is phosphorylated by Hrr25 in vitro. We find that swi4, swi6, and hrr25 mutants, but not mbp1 mutants, are sensitive to hydroxyurea and the DNA-damaging agent methyl methane-sulfonate and are defective in the transcriptional induction of a subset of DNA damage-inducible genes. Both the sensitivity of swi6 mutants to methyl methanesulfonate and hydroxyurea and the transcriptional defect of hrr25 mutants are rescued by overexpression of SWI4, implicating the SBF complex in the Hrr25/Swi6-dependent response to DNA damage.

Neisserial porins induce B lymphocytes to express costimulatory B7-2 molecules and to proliferate

The neisserial porins are the major protein components of the outer membrane of the pathogenic Neisseria (N. meningitidis and N. gonorrhoeae). They have been shown to be able to enhance the immune response to poorly immunogenic substances (e.g., polysaccharides, peptides, glycolipids, etc.). To explore the basis of their potent adjuvant activity, the effect of the neisserial porins on T-B cell interactions and T cell costimulation was examined. Neisserial porins increased the surface expression of the costimulatory ligand B7-2 (CD86) but did not affect the expression of B7-1 (CD80). In addition, incubation with the neisserial porins increased the T lymphocyte costimulatory ability of B lymphocytes, which was inhibited by anti-B7-2 but not anti-B7-1 monoclonal antibodies. Upregulation of B7-2 on the surface of B lymphocytes may be the mechanism behind the immunopotentiating activity of neisserial porins.

Mouse preimplantation embryo development in vitro: effect of sodium concentration in culture media on RNA synthesis and accumulation and gene expression

Results of previous studies indicate that culture of preimplantation mouse embryos in SOM medium containing 85 mM NaCl promotes better development in vitro, as well as supporting higher rates of protein synthesis, when compared to culture in SOM containing 125 mM NaCl (Anbari and Schultz, 1993, Mol Reprod Dev 35:24-28; Biggers et al., 1993, Mol Reprod Dev 34:380-390). In the present study we compare the effect of culturing embryos in these 2 media on several aspects of RNA synthesis and gene expression in order to determine whether the reduced development in SOM containing 125 mM NaCl and lower rates of protein synthesis are correlated with decreases in RNA synthesis and stability and changes in gene expression. Although no apparent differences in the metabolism of [3H]uridine to UMP, UDP, and UTP and its incorporation into total RNA are observed when 2-cell embryos are cultured to the morula stage in either medium, a 20% decrease in the rate of mRNA synthesis is found when embryos are cultured in SOM containing 125 mM NaCl. In addition, pulse-chase experiments reveal that total mRNA is less stable when the embryos are cultured in SOM containing 125 mM NaCl. Using a reverse transcription-polymerase chain reaction to assay for changes in the relative amounts of specific mRNAs, the relative amounts of mRNAs for IGF-I and IGF-II and their cognate receptors are dramatically reduced in embryos cultured in SOM containing 125 mM NaCl, whereas only a mild reduction is observed in the relative amount of actin mRNA. In contrast, when freshly isolated morulae are cultured to the blastocyst stage in either of these 2 media, similar amounts of these mRNAs are observed. Last, high-resolution, 2-dimensional gel electrophoresis reveals significant changes in the pattern of protein synthesis when the embryos are cultured in SOM containing 125 mM NaCl. Results of these experiments suggest that culture of embryos in medium containing lower concentrations of NaCl that are normally present in various culture media results in higher rates of mRNA synthesis and greater mRNA stability. These changes in RNA synthesis may underlie, at least in part, the improved development in vitro that is fostered by SOM containing 85 mM NaCl.

Interaction of yeast Rvs167 and Pho85 cyclin-dependent kinase complexes may link the cell cycle to the actin cytoskeleton

BACKGROUND

. PHO85 encodes the catalytic subunit of a cyclin-dependent kinase (Cdk) in budding yeast and functions in phosphate and glycogen metabolism. Pho85 associated with the G1 cyclins Pcl1 and Pcl2 is also required for cell cycle progression in the absence of the Cdc28 cyclins Cln1 and Cln2. Loss of Pcl1, Pcl2 and related Pho85 cyclins results in budding defects, suggesting that Pcl-Pho85 complexes function in cell morphogenesis early in the cell cycle; their precise role is not clear, however.

RESULTS

. To identify targets for Pcl-Pho85 kinases, we performed yeast two-hybrid interaction screens using Pcl2 and the related cyclin Pcl9. We identified RVS167, a gene involved in endocytosis, organization of the actin cytoskeleton, and cell survival after starvation. Like rvs167Delta mutants, pho85 mutants or strains deleted for the Pcl1,2-type Pho85 cyclins showed abnormal cell morphology on starvation, sensitivity to salt, random budding in diploids, and defects in endocytosis and in the actin cytoskeleton. Overexpression of Rvs167 in wild-type cells caused morphological abnormalities and growth arrest at high temperatures; these phenotypes were exacerbated by deleting PHO85. Rvs167 has a Src homology 3 (SH3) domain and five potential Pho85 phosphorylation sites; recombinant Rvs167 was phosphorylated by the Pcl2-Pho85 kinase in vitro. Maximal phosphorylation of Rvs167 in vivo required Pho85 and the Pcl1,2-type cyclins.

CONCLUSIONS

. Rvs167 interacts with Pho85 cyclins and is implicated as a target of Pho85 kinases in vivo. Our results identify a connection between Cdks and the actin cytoskeleton; interaction of Rvs167 and Pcl-Pho85 Cdks might contribute to actin cytoskeleton regulation in response to stresses such as starvation.

Overexpression of CuZnSOD in coronary vascular cells attenuates myocardial ischemia/reperfusion injury

Superoxide dismutase scavenges oxygen radicals, which have been implicated in ischemia/reperfusion (I/R) injury in the heart. Our experiments were designed to study the effect of a moderate increase of copper/zinc superoxide dismutase (CuZnSOD) on myocardial I/R injury in TgN(SOD1)3Cje transgenic mice. A species of 0.8 kb human CuZnSOD mRNA was expressed, and a 273% increase in CuZnSOD activity was detected in the hearts of transgenic mice with no changes in the activities of other antioxidant enzymes. Furthermore, immunoblot analysis revealed no changes in the levels of HSP-70 or HSP-25 levels. Immunocytochemical study indicated that there was increased labeling of CuZnSOD in the cytosolic fractions of both endothelial cells and smooth muscle cells, but not in the myocytes of the hearts from transgenic mice. When these hearts were perfused as Langendorff preparations for 45 min after 35 min of global ischemia, the functional recovery of the hearts, expressed as heart rate x LVDP, was 48 +/- 3% in the transgenic hearts as compared to 30 +/- 5% in the nontransgenic hearts (p <.05). The improved cardiac function was accompanied by a significant reduction in lactate dehydrogenase release from the transgenic hearts. Our results demonstrate that overexpression of CuZnSOD in coronary vascular cells renders the heart more resistant to I/R injury.

Regulation of transcription at the Saccharomyces cerevisiae start transition by Stb1, a Swi6-binding protein

In Saccharomyces cerevisiae, gene expression in the late G(1) phase is activated by two transcription factors, SBF and MBF. SBF contains the Swi4 and Swi6 proteins and activates the transcription of G(1) cyclin genes, cell wall biosynthesis genes, and the HO gene. MBF is composed of Mbp1 and Swi6 and activates the transcription of genes required for DNA synthesis. Mbp1 and Swi4 are the DNA binding subunits for MBF and SBF, while the common subunit, Swi6, is presumed to play a regulatory role in both complexes. We show that Stb1, a protein first identified in a two-hybrid screen with the transcriptional repressor Sin3, binds Swi6 in vitro. The STB1 transcript was cell cycle periodic and peaked in late G(1) phase. In vivo accumulation of Stb1 phosphoforms was dependent on CLN1, CLN2, and CLN3, which encode G(1)-specific cyclins for the cyclin-dependent kinase Cdc28, and Stb1 was phosphorylated by Cln-Cdc28 kinases in vitro. Deletion of STB1 caused an exacerbated delay in G(1) progression and the onset of Start transcription in a cln3Delta strain. Our results suggest a role for STB1 in controlling the timing of Start transcription that is revealed in the absence of the G(1) regulator CLN3, and they implicate Stb1 as an in vivo target of G(1)-specific cyclin-dependent kinases.

Steroid sulphatase inhibitors for breast cancer therapy

In contrast to aromatase inhibitors, which are now in clinical use, the development of steroid sulphatase (STS) inhibitors for breast cancer therapy is still at an early stage. STS regulates the formation of oestrone from oestrone sulphate (E1S) but also controls the hydrolysis of dehydroepiandrosterone sulphate (DHEA-S). DHEA can be reduced to 5-androstenediol (Adiol), a steroid with potent oestrogenic properties. The active pharmacophore for potent STS inhibitors has now been identified, i.e. a sulphamate ester group linked to an aryl ring. This has led to the development of a number of STS inhibitors, some of which are due to enter Phase I trials in the near future. Such first generation inhibitors include the tricyclic coumarin-based 667 COUMATE. Aryl sulphamates, such as 667 COUMATE, are taken up by red blood cells (rbc), binding to carbonic anhydrase II (CA II), and transit the liver without undergoing first-pass inactivation. 667 COUMATE is also a potent inhibitor of CA II activity with an IC50 of 17 nM. Second generation STS inhibitors, such as 2-methoxyoestradiol bis-sulphamate (2-MeOE2bisMATE), in addition to inhibiting STS activity, also inhibit the growth of oestrogen receptor negative (ER-) tumours in mice and are anti-angiogenic. As the active pharmacaphores for the inhibition of aromatase and STS are now known it may be possible to develop third generation inhibitors that are capable of inhibiting the activities of both enzymes. Whilst exploring the potential of such a strategy it was discovered that 667 COUMATE possessed weak aromatase inhibitory properties with an IC50 of 300 nM in JEG-3 cells. The identification of potent STS inhibitors will allow the therapeutic potential of this new class of drug to be explored in post-menopausal women with hormone-dependent breast cancer. Second generation inhibitors, such as 2-MeOE2bisMATE, which also inhibit the growth of ER- tumours should be active against a wide range of cancers.

A protein encoded by a group I intron in Aspergillus nidulans directly assists RNA splicing and is a DNA endonuclease

Some group I introns self-splice in vitro, but almost all are thought to be assisted by proteins in vivo. Mutational analysis has shown that the splicing of certain group I introns depends upon a maturase protein encoded by the intron itself. However the effect of a protein on splicing can be indirect. We now provide evidence that a mitochondrial intron-encoded protein from Aspergillus nidulans directly facilitates splicing in vitro. This demonstrates that a maturase is an RNA splicing protein. The protein-assisted reaction is as fast as that of any other known group I intron. Interestingly the protein is also a DNA endonuclease, an activity required for intron mobilization. Mobile elements frequently encode proteins that promote their propagation. Intron-encoded proteins that also assist RNA splicing would facilitate both the transposition and horizontal transmission of introns.

Determination of (+)-catechin in plasma by high-performance liquid chromatography using fluorescence detection

A high-performance liquid chromatographic method, using fluorescence detection, was developed for the determination of (+)-catechin in rabbit plasma. The procedure involved the precipitation of plasma protein using acetonitrile, followed by solid-phase adsorption onto alumina. After washing with water and methanol, the residue was vortex-mixed with perchloric acid solution to release the adsorbed (+)-catechin. Separation was performed on a reversed-phase column using an eluent consisting of phosphoric acid solution with 12% acetonitrile. The excitation and emission wavelengths were set at 280 and 310 nm, respectively. The retention times for (+)-catechin and the internal standard (deoxyhigenamine) were 6.87 and 8.47 min respectively, without any interference. Validations of accuracy and precision were satisfactory in both within- and between-run assays. All coefficients of variance were less than 6% and mean relative errors were within +/- 3.75%. The average recovery was 73.77%. The limit of detection and quantitation were 1 ng and 0.02 micrograms/ml, respectively. Application of this method was successfully assessed by intravenous administration of a 15 mg/kg dose of (+)-catechin in rabbits. This new method provides a simple, specific and sensitive determination for (+)-catechin in rabbit plasma and is suitable for pharmacokinetic studies.

Normal anatomy and common labral lesions at MR arthrography of the shoulder

MR arthrography of the shoulder is the most accurate imaging modality in demonstrating abnormalities of the glenoid labrum and associated structures. Tears of the labrum, the capsule or the gleno-humeral ligaments can lead to pain, catching, popping or instability. The anatomy of this region is complex. We present the normal anatomy of the glenoid labrum, biceps anchor and gleno-humeral ligaments together with their normal variants and then describe common labral-ligamentous pathologies.

The role of B/T costimulatory signals in the immunopotentiating activity of neisserial porin

A T cell-dependent immune response to group C meningococcal capsular polysaccharide (CPS) can be elicited when CPS is conjugated to the class 3 neisserial porin (CPS-porin). Treatment of CPS-porin-immunized mice with B7-2 blocking monoclonal antibody (MAb) caused a dramatic reduction in the CPS-specific IgG response, treatment with anti-B7-1 MAb had no effect, and concurrent blockade of B7-1 and B7-2 resulted in a synergistic abrogation of the CPS-specific IgG response while the CPS IgM response was unaffected. Anti-CD40L MAb treatment caused a significant reduction of both CPS-specific IgG and IgM levels. In contrast, blockade of CTLA4 interactions resulted in increases in both CPS IgG and IgM responses in CPS-porin-immunized mice. These data support the hypothesis that the ability of neisserial porins to improve the immune response to poorly immunogenic antigens (e.g., polysaccharides) is related to porin-induced increases in B7-2 expression on antigen-presenting cells and enhanced B/T cell interactions.

Observation of muon neutrino disappearance with the MINOS detectors in the NuMI neutrino beam

This Letter reports results from the MINOS experiment based on its initial exposure to neutrinos from the Fermilab NuMI beam. The rates and energy spectra of charged current nu(mu) interactions are compared in two detectors located along the beam axis at distances of 1 and 735 km. With 1.27 x 10(20) 120 GeV protons incident on the NuMI target, 215 events with energies below 30 GeV are observed at the Far Detector, compared to an expectation of 336+/-14 events. The data are consistent with nu(mu) disappearance via oscillations with |Delta(m)2/32|=2.74 +0.44/-0.26 x10(-3)eV(2) and sin(2)(2theta(23))>0.87 (68% C.L.).

The maturase encoded by a group I intron from Aspergillus nidulans stabilizes RNA tertiary structure and promotes rapid splicing

The AnCOB group I intron from Aspergillus nidulans self-splices, providing the Mg2+ concentration is >/= 15 mM. The splicing reaction is greatly stimulated by a maturase protein encoded within the intron itself. An initial structural and biochemical analysis of the splicing reaction has now been performed. The maturase bound rapidly to the precursor RNA (kon approximately 3 x 10(9) M(-1) min(-1)) and remained tightly bound (koff </= 0.04 min(-1)). The catalytic step of 5' splice-site cleavage occurred at a rate of up to 11 min(-1) under single turnover conditions. The maturase-assisted reaction of heat-denatured RNA proceeded at a rate of about 1 min(-1), arguing that there are early steps of folding that cannot be readily facilitated by the protein. pH analysis revealed a biphasic profile with a pKa of 7.0. The rate of the maturase-assisted reaction was independent of the Mg2+ concentration down to 3 mM. Self-splicing in optimal Mg2+ (>/= 150 mM) was tenfold slower, in part because of the existence of an equilibrium between folded and partially folded RNA. In contrast, the maturase very effectively stabilized tertiary structure in 5 mM Mg2+, a noticeable example being an interaction between the P8 helix and a GNRA sequence that constitutes the L2 terminal loop of the P2 helix. Formation of the 5' splice-site recognition helix was assisted by either the maturase or high concentrations of Mg2+. The maturase was required during splicing so it is not a true chaperone. However, RNase protection assays and kinetic studies suggest that the maturase recognizes and facilitates folding of an intron with limited tertiary structure and even incomplete secondary structure.

Chemical modification of bovine transducin: effect of fluorescein 5'-isothiocyanate labeling on activities of the transducin alpha subunit

Fluorescein 5'-isothiocyanate (FITC) was used to modify the lysine residues of bovine transducin (T), a GTP-binding protein involved in phototransduction of rod photoreceptor cells. The incorporation of FITC showed a stoichiometry of approximately 1 mol of FITC/mol of transducin. The labeling was specific for the T alpha subunit. There was no significant incorporation on the T beta gamma subunit. The modification had no effect on the transducin-rhodopsin interaction or on the binding of guanosine 5'-(beta, gamma-imidotriphosphate) [Gpp(NH)p] to transducin in the presence of photolyzed rhodopsin. The dissociation of the FITC-transducin-Gpp(NH)p complex from rhodopsin membrane remained unchanged. However, the intrinsic GTPase activity of T alpha and its ability to activate the cGMP phosphodiesterase were diminished by FITC modification. The rate of FITC labeling of the transducin-Gpp(NH)p complex was about 3-fold slower than that of transducin. Limited tryptic digestion and peptide mapping were used to localize the FITC labeling site. The majority of the FITC label was on the 23-kilodalton fragment, and a minor amount was on the 9-kilodalton fragment of the T alpha subunit. These results indicate that FITC labeling does not alter the activation of transducin by photolyzed rhodopsin but does affect the GTP hydrolytic activity as well as the GTP-induced conformational change of T alpha, which ultimately leads to the activation of cGMP phosphodiesterase.

T lymphocyte response to Neisseria gonorrhoeae porin in individuals with mucosal gonococcal infections

T lymphocytes from a majority of patients with urogenital gonococcal disease (67%-80%) proliferated on incubation with gonococcal porin (Por), compared with minimal induced proliferation of T lymphocytes from normal volunteers. A significant increase in Por-specific interleukin (IL)-4-producing CD4+ T helper lymphocytes was seen in patients with mucosal gonococcal disease and not in normal controls. Similar results were observed in CD8+ T lymphocytes from these patients. There was no measured increase in IL-2, IL-10, IL-12, interferon-gamma, or tumor necrosis factor-alpha production by T lymphocytes from infected subjects on incubation with Por. Concomitant increases in IL-4 production in T lymphocytes from infected subjects expressing the mucosal addresin VLAalpha4/beta7 on their surface were also observed on Por incubation, but the increases were similar in T lymphocytes that were VLAalpha4/beta7 negative. In conclusion, mucosal gonococcal disease can induce Por-specific circulating T lymphocytes with a Th2 phenotype, and a portion of these Por-specific T lymphocytes can potentially traffic to mucosal surfaces.

Evidence for changing of cosmic ray composition between 10(17) and 10(18) eV from multicomponent measurements

The average mass composition of cosmic rays with primary energies between 10(17) and 10(18) eV has been studied using a hybrid detector consisting of the High Resolution Fly's Eye (HiRes) prototype and the MIA muon array. Measurements have been made of the change in the depth of shower maximum and the muon density as a function of energy. The results show that the composition is changing from a heavy to lighter mix as the energy increases.

Effects of olfactory bulbectomy on NMDA receptor density in the rat brain:

Olfactory bulbectomy (OBX) transects the glutamatergic efferents from the olfactory bulbs, and the changes of glutamatergic N-methyl-D-aspartate (NMDA) receptor-mediated function are though to be involved in the behavioral deficits seen in OBX rats. In the present study, irritability scores in OBX male Wistar rats were correlated with discrete regional effects on NMDA receptor function measured using a [3H] MK-801 binding assay. Irritability scores, measured before and for 2 weeks after OBX, showed a gradual increase in irritability after OBX. A reduction of the NMDA receptor density was observed in the cerebral cortex and amygdala 16 days after OBX, but not in the striatum, olfactory tubercle, entorhinal cortex, and hippocampus. These results demonstrate that OBX causes changes in the NMDA receptor system in certain brain regions and suggest that these changes may be responsible for the behavioral deficits of OBX rats.

Early complement components enhance neutralization of Chlamydia trachomatis infectivity by human sera

Immunoglobulin G in human serum neutralizes chlamydial infectivity in vitro. Complement-intact, C5-depleted, and C8-depleted human serum all have significantly more neutralizing activity than serum heated to inactivate early components of complement. Cobra venom factor, an analog of human C3b, enhances neutralization of antichlamydial immunoglobulin G in the absence of early complement components.