Optical associative memory using an orthogonalized hologram

A two-dimensional orthogonal model of optical associative memory for storage of nonnegative patterns using a single hologram is presented. Two sets of patterns after prior orthogonal processing are composed and used for hologram recording, which permits the sequential holographic recordings to be carried on spatially separated regions of the recording material. High diffraction efficiency of the hologram is achieved. Computer simulations and optical demonstrations are also given.

Antioxidation activity of tetrahydrobiopterin in pheochromocytoma PC 12 cells

Rat pheochromocytoma PC 12 cells are susceptible to the oxidative toxicity caused by H2O2, nitrofurantoin, dopamine, and xanthine/xanthine oxidase reaction. The cytotoxicities of these agents are greatly reduced by the simultaneous presence of 0.1 mM tetrahydrobiopterin (BH4), 3 units/ml horseradish peroxidase, 0.2 mM NADH, and 0.1 units/ml sheep liver dihydropteridine reductase (DHPR). Individually, BH4, NADH and DHPR have no protection against H2O2 toxicity in PC 12 cells. Peroxidase alone offers 58% of protection if cells are incubated in the medium but only 3% in Dulbecco's phosphate buffered saline. The efficiency of the BH4-mediated antioxidation system in PC 12 cells is equal to or better than ascorbic acid and catalase, depending on the source of the reactive O2 species (ROS). The reactions responsible for the BH4-antioxidation system may consist of the non-enzymatic and the peroxidase-catalyzed reduction of H2O2 to H2O by BH4 and the regeneration of BH4 by DHPR using NADH as the cofactor. The components of this defence mechanism against ROS are all normal cellular constituents and are ubiquitous in nature. This DHPR-catalyzed redox cycling of BH4 may constitute an as yet little-known antioxidation system in mammalian cells.

Fleroxacin combined with rifampin

We determined the effect of the combination of rifampin and fleroxacin against Enterobacteriaceae and streptococcal species. None of the 65 isolates tested by checkerboard assay demonstrated synergy, 12% of isolates showed an additive effect; 86.7% were indifferent, and only 1 isolate showed antagonism. The mean FIC was 1.2. When using 2 and 8 micrograms/ml of rifampin, fleroxacin MICs of 285 isolates of Enterobacteriaceae, Pseudomonas aeruginosa, Haemophilus influenzae, staphylococci, streptococci, Bacteroides, and Clostridium were not increased, but synergy was not demonstrated. Time-kill studies against Escherichia coli, P. aeruginosa, Enterobacter cloacae, Staphylococcus aureus, and Enterococcus faecalis failed to show increased killing when the two agents were present at one-half the MBC. The fleroxacin-rifampin interaction is one of indifference but provides coverage for species not adequately inhibited by fleroxacin.

Diarrhoea surveillance in children aged under 5 years in a rural area of Hebei Province, China

A surveillance of diarrhoeal diseases in children aged under five years was carried out from March 1986 to February 1987 in a rural area of Hebei Province, China. Using a cluster sampling method, 270 study children were selected from 30 villages to represent a population of 105,405. Parents noted episodes of diarrhoea in children on a calender using a given definition of diarrhoea. The findings were verified by trained village doctors and were recorded monthly in the county Health and Anti-epidemic Stations. Stools of diarrhoea-affected children were examined to detect causal agents of diarrhoea, once in each of four seasons of the year. Of the 270 children, 218 (80.74%) suffered from one or more than one attacks of diarrhoea with a 95% confidence interval between 75.94% and 85.54%. There was no death due to diarrhoea. The diarrhoeal incidence in children of 3-4-year age group was significantly less than that in the children of less than 3 years (p less than 0.05). In the children with diarrhoea, the number of mean episodes was 3.15 per child/year, and the total mean course of suffering was 14 days per child/year. The ratio of diarrhoeal episodes in spring, summer, autumn, and winter was about 2.5:5:2:1. July was the month of highest occurrence of diarrhoea (146; 21.28% of all episodes). The epidemiological parameters of the disease declined with the growing age of the children, and there was no gender-specific preponderance in the number of episodes. During the whole year, 21.7% of the diarrhoeal episodes were due to bacterial pathogens, 4% of the episodes were due to rotavirus, and 3.65% episodes were associated with the detection of Trichomonas hominis.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple tandem promoters of the major outer membrane protein gene (omp1) of Chlamydia psittaci

The transcription of omp1, the gene encoding the major outer membrane protein, was studied for two strains of Chlamydia psittaci, guinea pig inclusion conjunctivitis (GPIC) and mouse pneumonitis (Mn). The transcriptional initiation sites for the omp1 of each strain were mapped by S1 nuclease and primer extension analyses. Three different sizes of omp1 transcripts were observed for GPIC and four were observed for Mn. The production of these transcripts appeared to be the consequence of multiple tandem promoters. The order in which the omp1 RNA transcripts appeared during the growth cycle of the C. psittaci strains was found to differ from that of C. trachomatis.

Chlamydia trachomatis-host cell interactions: role of the chlamydial major outer membrane protein as an adhesin

The major outer membrane protein (MOMP) of Chlamydia trachomatis is characterized by four symmetrically spaced variable domains (VDs I to IV) whose sequences vary among serotypes. The surface-exposed portions of these VDs contain contiguous sequences that are both serotyping determinants and in vivo target sites for neutralizing antibodies. Previous studies using surface proteolysis of C. trachomatis B implicated VDs II and IV of the MOMP of this serotype in the attachment of chlamydiae to host cells. In this study, we used monoclonal antibodies (MAbs) specific to antigenic determinants located in VDs II and IV of the MOMP of serotype B to further investigate the role of the MOMP in the attachment of chlamydiae to host cells. MABs specific to serotype- and subspecies-specific epitopes located in exposed VDs II and IV, respectively, neutralized chlamydial infectivity for hamster kidney cells by blocking chlamydial attachment. We radioiodinated these MAbs and used them to determine the number and topology of the surface-exposed VDs II and IV epitopes on chlamydial elementary bodies. VDs II and IV each comprised approximately 2.86 x 10(4) negatively charged sites and were in proximity on the chlamydial cell surface. These studies suggest that the MAbs blocked chlamydial attachment by inhibiting electrostatic interactions with host cells. We examined the effects of thermal inactivation on both chlamydial attachment and conformation of the MOMP. Heat-inactivated chlamydiae failed to attach to host cells and exhibited a conformational change in an inaccessible invariant hydrophobic nonapeptide sequence located within VD IV of the MOMPs of C. trachomatis serotypes. These findings suggest that in addition to electrostatic interactions, a common hydrophobic component of the MOMP also contributes to the binding of chlamydiae to host cells. Thus, we propose that the MOMP functions as a chlamydial adhesin by promoting nonspecific (electrostatic and hydrophobic) interactions with host cells. Surface-accessible negatively charged VDs appear to be important in electrostatic binding, while the invariant region of VD IV may provide a subsurface hydrophobic depression which further promotes binding of chlamydiae to host cells through hydrophobic interactions.

[Effective measures to control air pollution from burning coal]

We designed "passive measures" to control air pollution from burning coal in living rooms and have found the results satisfactory in reducing air pollution. The measures were simple, feasible and effective. They can be widely applied in the cold regions where living rooms are heated by burning coal.

Characterization of murine monoclonal and murine, rabbit, and human polyclonal antibodies against chlamydial lipopolysaccharide

Murine monoclonal and rabbit, murine, and human polyclonal antibodies against chlamydial lipopolysaccharide (LPS) were characterized by the passive hemolysis and passive hemolysis inhibition assays and by absorption experiments with LPSs of Chlamydia psittaci, Chlamydia trachomatis, and a recombinant strain of Salmonella minnesota Re (r595-207) expressing the chlamydia-specific LPS epitope, as well as natural and synthetic partial structures of chlamydial LPS. Eleven monoclonal antibodies of the immunoglobulin M and G classes were characterized as chlamydia-specific by their failure to react with Re-type LPS, binding to a similar epitope for which the trisaccharide alpha-3-deoxy-D-manno-2-octulosonic acid (KDO)-(2-8)-alpha-KDO-(2-4)-alpha-KDO was an absolute prerequisite. For optimal binding, parts of the lipid A moiety were also involved; however, phosphoryl and ester-linked acyl groups and the reducing glucosamine residue of lipid A were dispensable. A similar antibody specificity was detected in lapine and murine hyperimmune sera after immunization with chlamydia, in addition to those recognizing more complex (e.g., those requiring the presence of phosphoryl residues) and less complex epitopes. Among the latter were those cross-reacting with Re-type LPS, which could be removed by absorption. The titers of different antibody specificities, in particular the ratio of chlamydia-specific to cross-reactive antibodies, present in murine polyclonal antisera depended on the immunization protocol. The preferential formation of chlamydia-specific antibodies was observed after immunization with liposome-incorporated immunogens. Human sera from patients with suspected genital chlamydial infections were also found to contain chlamydia-specific and cross-reactive antibodies, the latter of which could be removed by absorption with Re-type LPS.

Use of monoclonal antibodies to glial fibrillary acidic protein in the cytologic diagnosis of brain tumors

Monoclonal antibodies were used to immunocytochemically demonstrate glial fibrillary acidic protein (GFAP) in 174 smear preparations of brain tumor tissue in order to investigate the presence and distribution of GFAP in a variety of intracranial tumors and to evaluate the value of this technique in the cytodiagnosis of brain tumors. GFAP-positive cells were found in the astrocytic tumors and in some of the oligodendrogliomas, ependymomas and medulloblastomas. In contrast, schwannomas, meningiomas, a primary lymphoma, a hemangiopericytoma pituitary adenomas, germinomas and metastatic tumors were negative for GFAP. The cytodiagnostic accuracy of the 174 brain tumors was raised from 90.8% to 97.1% when GFAP-immunoperoxidase staining was employed to aid the routine cytologic diagnosis. These findings indicate that immunoperoxidase staining for GFAP can be successfully applied to cytologic specimens and is a useful adjunct to routine cytologic diagnosis.

Cloning and sequence analysis of the major outer membrane protein genes of two Chlamydia psittaci strains

We cloned and sequenced the gene encoding the major outer membrane protein (MOMP) of two Chlamydia psittaci strains, guinea pig inclusion conjunctivitis (GPIC) strain 1, and meningopneumonitis (Mn) strain Cal-10. Intraspecies alignment of the two C. psittaci MOMP genes revealed 80.6% similarity, and interspecies comparison of C. trachomatis and C. psittaci MOMP genes yielded about 68% similarity. As found previously for C. trachomatis MOMP sequences, stretches of predominantly conserved sequences of GPIC and Mn MOMPs were interrupted by four variable domains whose locations were identical to those of C. trachomatis MOMPs. Seven of eight cysteine residues were found at precisely the same positions in GPIC, Mn, and C. trachomatis MOMPs, emphasizing their importance in structure and function of the protein. Collectively, these results indicate that C. psittaci and C. trachomatis MOMP genes diverged from a common ancestor.

Nucleotide and deduced amino acid sequences for the four variable domains of the major outer membrane proteins of the 15 Chlamydia trachomatis serovars

The amino acid sequences of major outer membrane proteins (MOMPs) from Chlamydia trachomatis serovars A, B, C, L1, and L2 are predominantly conserved but have four variable domains (VDs) in which major neutralizing and serotyping antigenic determinants are located. Because these MOMP VDs are primarily responsible for antigenic differences between serovars and are associated with important immunological and biological properties, we undertook studies focused on defining these sequences within the MOMPs of all 15 C. trachomatis serovars. We used oligonucleotide primer extension sequencing of MOMP mRNA to determine the nucleotide and deduced amino acid sequences of the four MOMP VDs of the 15 C. trachomatis serovars. Comparative amino acid sequence homologies of all four domains separated the serovars into three groups: group 1, serovars B, Ba, D, E, L1, and L2; group 2, serovars G and F; and group 3, serovars A, C, H, I, J, K, and L3. Hydrophilicity and charge values for each domain were determined. The MOMP VDs of given serovars with the greatest total hydrophilicity and charge values were found to be the location of antigenic determinants recognized by MOMP-specific monoclonal antibodies. These findings should be useful for predicting MOMP antigenic determinants and testing the antigenic properties of these VDs by using synthetic peptides corresponding to each MOMP VD. The potential usefulness of the VD sequence information is discussed in relation to the development of defined synthetic peptides and oligonucleotides that may be used to develop new serological and diagnostic assays for C. trachomatis infections.

Human liver GTP cyclohydrolase I: purification and some properties

Human liver guanosine triphosphate (GTP) cyclohydrolase I has been purified more than 1,700-fold to what appears to be homogeneity. The active enzyme complex has an estimated molecular weight of 453,000 +/- 11,500 by gel filtration chromatography. It consists of a polypeptide of 149,000 +/- 4,000 mol wt by SDS-polyacrylamide gel electrophoresis. The activity of the enzyme is heat stable and is inhibited by di- and trivalent cations. The enzyme has an optimum pH of 7.7 in sodium phosphate buffer. It uses GTP as a sole substrate, with a Km of 116 microM.

Viral etiology of cervical carcinoma. Human papilloma virus and herpes simplex virus type 2

The possible role of human papilloma virus (HPV) and herpes simplex virus type 2 (HSV-2) in the viral etiology of cervical carcinoma was investigated a series of cervical lesions were studied for the presence of HPV and HSV-2 DNA sequences as well as HPV and HSV-2 antigens by DNA dot blot hybridization technique and high-specificity PAP staining method. The results obtained were correlated with the histologic diagnosis. HPV 16 DNA sequences detected in cervical carcinoma biopsies were 43%, whereas HSV-2 DNA sequences were only 8%. HPV antigens detected in cervical dysplasia were 31%, whereas those detected in cervical carcinoma and cervicitis were the least. HSV-2 antigens were detected in chronic cervicitis, dysplasia and cervical carcinoma. The difference in positive rate between the cervical carcinoma and cervicitis groups was statistically significant, (chi-square test, P less than 0.01). No HPV DNA and HSV-2 DNA sequences were found in the same specimen, although both HPV DNA sequences and HSV-2 antigens were found in the same sample in some cases. The results indicate that the viral etiology of cervical carcinoma may be multifactorial. Both HSV-2 and HPV may be associated with cervical carcinoma, but the mechanisms involved are different. HSV-2 and HPV may act synergistically in the development of cervical carcinoma.

Protective monoclonal antibodies to Chlamydia trachomatis serovar- and serogroup-specific major outer membrane protein determinants

Monoclonal antibodies exhibiting Chlamydia trachomatis serovar specificity (serovar A, B-Ba, or C) and serogroup specificity (B, intermediate, or C serogroup) were produced and characterized. These antibodies reacted with the major outer membrane protein, recognized epitopes located at the chlamydial cell surface, and passively neutralized chlamydial toxicity for mice. The antibodies should be useful reagents for defining the molecular structure of these protective epitopes, a necessary step toward the development of a subunit or recombinant C. trachomatis vaccine.

Regulation of GTP cyclohydrolase I and dihydropteridine reductase in rat pheochromocytoma PC 12 cells

The addition of 8-bromo cyclic AMP, forskolin, theophylline, and 3-isobutyl-1-methylxanthine to the medium of PC 12 cells resulted in an increase in GTP cyclohydrolase I activity, but had no effect on dihydropteridine reductase activity, except theophylline which caused a decrease in dihydropteridine reductase activity at 96 h. GTP cyclohydrolase I activity peaked at 24 h and returned to normal 96 h after drug treatment. Cycloheximide decreased GTP cyclohydrolase I activity at 48 and 96 h, but had little effect on dihydropteridine reductase activity. The addition of reserpine selectively increased only GTP cyclohydrolase I activity. The addition of tetrahydrobiopterin and sepiapterin, however, coordinately inhibited both GTP cyclohydrolase I and dihydropteridine reductase activities. It appears that GTP cyclohydrolase I activity in PC 12 cells is regulated by cyclic AMP stimulation and by end-product inhibition, whereas dihydropteridine reductase activity is only subject to pterin inhibition.

Differential effect of trypsin on infectivity of Chlamydia trachomatis: loss of infectivity requires cleavage of major outer membrane protein variable domains II and IV

The initial interaction of chlamydiae with host cells is not well understood. Chlamydial cell surface components that function in attachment are key virulence factors, and their identification is critical for understanding the pathogenic strategies of this very successful parasite. We used trypsin proteolysis of chlamydiae to define surface components that function in chlamydia-host cell interactions. We found that trypsin had a differential effect on the infectivity of Chlamydia trachomatis serovars B and L2 for HeLa 229 cells. Trypsin treatment resulted in a significant loss of attachment and infectivity of serovar B but had no effect on the infectivity of serovar L2. Fluorograms of chlamydiae metabolically labeled with 14C-amino acids and treated with trypsin showed that the major outer membrane protein (MOMP) of both serovars was cleaved. Evidence for two trypsin cleavage sites was found for the serovar B MOMP. One cleavage site was located between lysine 145 and valine 146 in variable domain (VD) II of the protein. The second site was located between lysine 309 and threonine 310 in VD IV. In contrast, the serovar L2 MOMP was cleaved only at lysine 309 in VD IV. These results suggest a functional role for MOMP in chlamydial attachment and implicate VDs II and IV of MOMP in this interaction.

Mapping antigenic domains expressed by Chlamydia trachomatis major outer membrane protein genes

Chlamydia trachomatis is an obligate prokaryotic intracellular pathogen of humans that infects mucosal epithelial cells. Exposed domains of its major outer membrane protein (MOMP) are both serotyping and protective antigenic determinants. To identify these domains, we have cloned and epitope-mapped the genes of serovars A, C (C serogroup) and L2, B (B serogroup) with a panel of monoclonal antibodies (mAbs). Predominantly conserved regions of the genes of both serogroups are interspersed with four short variable domains (I-IV). Recombinant phage clones expressing specific MOMP antigenic determinants revealed that protective serotype-specific recognized epitopes in variable domains I and II. Protective subspecies and serogroup-specific mAbs recognized overlapping determinants in variable domain IV near the C terminus. A nonprotective species-specific mAb mapped to an invariant peptide of nine residues contained within variable domain IV. In the intact chlamydial organism of serovar B, variable domains II and IV were susceptible to proteolytic digestion, whereas both N and C termini were protected. These results suggest an arrangement of MOMP in the outer membrane in which three of the four variable domains are exposed to the outside and in which both N and C termini are presumably oriented toward the periplasmic space. This molecular analysis of MOMP antigenic determinants and their surface topology on intact chlamydiae will be useful toward the development of a recombinant subunit or synthetic chlamydial vaccine.

Inhibition of GTP cyclohydrolase I by pterins

Pterins inhibit rat liver GTP cyclohydrolase I activity noncompetitively. Reduced pterins, such as 7,8-dihydro-D-neopterin, (6R,S)-5,6,7,8-tetrahydro-D-neopterin, 7,8-dihydro-L-biopterin, (6R)-5,6,7,8-tetrahydro-L-biopterin, L-sepiapterin, and DL-6-methyl-5,6,7,8-tetrahydropterin are approximately 12-times more potent as inhibitors than are oxidized pterins, such as D-neopterin, L-biopterin, and isoxanthopterin. They are also 12-times more potent than folates, such as folic acid, dihydrofolic acid, (+/-)-L-tetrahydrofolic acid, and aminopterin. The Ki values for 7,8-dihydro-D-neopterin, 7,8-dihydro-L-biopterin, and (6R)-5,6,7,8-tetrahydro-L-biopterin are 12.7 microM, 14.4 microM, and 15.7 microM, respectively. These results suggest that mammalian GTP cyclohydrolase I may be regulated by its metabolic end products.

A compound catalytic model with both reversible and two-stage types and its applications in epidemiological study

A compound catalytic model with both reversible and two-stage types was studied. Using this model, the age-specific infection rate of hookworm in Changshou region was analysed. The fit of this model was checked by using the chi 2 test. It revealed that the data were fitted reasonably with the present model. The result indicated that this new model could be useful in epidemiological investigation.

The low-molecular-mass, cysteine-rich outer membrane protein of Chlamydia trachomatis possesses both biovar- and species-specific epitopes

We isolated, by hydroxylapatite high-performance liquid chromatography, 14- and 15-kilodalton (kDa), cysteine-rich outer membrane proteins from Chlamydia trachomatis TW-5/OT (serovar B) and LGV-434 (serovar L2), respectively. Monoclonal antibodies (MAbs) were generated against the purified proteins, and their specificities were determined by immunoblotting. MAb B-14k recognized an epitope located on the 14-kDa cysteine-rich protein of the TW-5/OT strain and was immunoreactive with a comigrating 14-kDa protein that was common to all trachoma biovar strains, but it did not react with the 15-kDa, cysteine-rich protein of LGV biovar strains. In contrast, MAb L2-15k, which recognized an epitope located on the 15-kDa protein of the LGV-434 strain, reacted with the 15- and 14-kDa, cysteine-rich proteins of both LGV and trachoma biovar strains, but did not react with related proteins of two Chlamydia psittaci strains. Thus, the low-molecular-mass, cysteine-rich outer membrane proteins of C. trachomatis possess antigenic determinants that are both biovar and species specific. Neither MAbB-14k nor MAb L2-15k was reactive by dot-blot assay when viable chlamydiae were used as test antigens, indicating that the cysteine-rich proteins are not accessible to antibody on the native chlamydial cell surface.

[Promoting effect of the Chinese medicinal herb, wikstroemia chamaedaphne and tung oil extracts on carcinoma of the uterine cervix induced by HSV-2 or methylcholanthrene (MCA) in mice]

The promoting effect of the Chinese medicinal herb, Wikstroemia chamaedaphne and Tung oil extracts (WC and HHPA) on carcinoma of uterine cervix induced by HSV-2 or MCA in mice was studied. The results showed that WC and HHPA extracts were not carcinogenic themselves. After carcinogen HSV-2 and MCA treatment, WC and HHPA were added separately. The inducing rates by HSV-2 increased from 7.4% to 21.1% and 26.3%, those by MCA increased from 56.5% to 82.8% and 84.4%. There was a significant difference between the combined groups and groups with HSV-2 or MCA only. The experimental results suggest that these two kinds of extracts play a promoting effect on carcinogenesis. The relation between the carcinogenesis of uterine cervix or nasopharynx and WC or HHPA extracts is discussed.

[Ultrastructure of brain tumor]

Ultrastructure of 15 brain tumors (6 astrocytomas, 5 meningiomas, 2 medulloblastomas and 2 Schwannomas) was observed by transmission electron microscope. In astrocytoma, both the fibrous and protoplasmic astrocytes were found. There were abundant capillaries among the tumor cells. The glia limitans outside the base membrane of certain capillaries were destroyed to different degrees. It indicates that the blood brain barrier may be damaged. Ultrastructurally, medulloblastoma cells may be divided into types I and II. The former was poorly differentiated but the latter was differentiated differently. Meningioma was similar to Schwannoma with complex cell membrane projections. The former had a lot of round mitochondria and filaments in the projections, between which desmosomes were observed. Schwannoma had the typical collagenous fibers among the projections. As to the epithelioid ultrastructure of meningioma, the authors speculate that the majority of meningiomas originate from the mesothelial cells of the arachnoid granulations.

Protective monoclonal antibodies recognize epitopes located on the major outer membrane protein of Chlamydia trachomatis

A panel of monoclonal antibodies (MAb) was generated against Chlamydia trachomatis serovar B, an etiologic agent of blinding trachoma. The specificities of MAb were determined by dot blot assay by using viable elementary bodies of 13 C. trachomatis serovars and two C. psittaci strains. The dot blot assay was used to identify those antigens that were unique and immunoaccessible on the chlamydial surface. MAb were identified that recognized bi-specific (serovars B and Ba) or subspecies-specific (various B complex serovars) surface-exposed antigenic determinants that were either resistant or sensitive to heat denaturation (56 degrees C, 30 min). All of the MAb recognized the major outer membrane protein as determined by either immunoblotting or radioimmunoprecipitation. MAb specific for immunoaccessible major outer membrane protein epitopes protected mice from toxic death after i.v. injection of B serovar elementary bodies and neutralized the infectivity of the organism for monkey eyes. In contrast, MAb reactive against non-immunoaccessible subspecies- or species-specific major outer membrane protein epitopes or against an immunoaccessible genus-specific epitope located on chlamydial lipopolysaccharide did not protect mice from toxic death or neutralize infectivity of the parasite for monkey eyes. These data suggest that those major outer membrane protein antigenic determinants that are serovar or serogroup specific and are accessible to antibody on the chlamydial cell surface may be useful as a recombinant subunit vaccine for trachoma.

Protective monoclonal antibodies recognize epitopes located on the major outer membrane protein of Chlamydia trachomatis

A panel of monoclonal antibodies (MAb) was generated against Chlamydia trachomatis serovar B, an etiologic agent of blinding trachoma. The specificities of MAb were determined by dot blot assay by using viable elementary bodies of 13 C. trachomatis serovars and two C. psittaci strains. The dot blot assay was used to identify those antigens that were unique and immunoaccessible on the chlamydial surface. MAb were identified that recognized bi-specific (serovars B and Ba) or subspecies-specific (various B complex serovars) surface-exposed antigenic determinants that were either resistant or sensitive to heat denaturation (56 degrees C, 30 min). All of the MAb recognized the major outer membrane protein as determined by either immunoblotting or radioimmunoprecipitation. MAb specific for immunoaccessible major outer membrane protein epitopes protected mice from toxic death after i.v. injection of B serovar elementary bodies and neutralized the infectivity of the organism for monkey eyes. In contrast, MAb reactive against non-immunoaccessible subspecies- or species-specific major outer membrane protein epitopes or against an immunoaccessible genus-specific epitope located on chlamydial lipopolysaccharide did not protect mice from toxic death or neutralize infectivity of the parasite for monkey eyes. These data suggest that those major outer membrane protein antigenic determinants that are serovar or serogroup specific and are accessible to antibody on the chlamydial cell surface may be useful as a recombinant subunit vaccine for trachoma.