Allergy to antibiotics: T-cell recognition of amoxicillin is HLA-DR restricted and does not require antigen processing

Allergic immune responses are initiated and maintained by T cells that recognize peptidic fragments of allergens in the context of major histocompatibility complex (MHC) class II molecules. An anomaly of this model exists in the T-cell response to haptens. Haptens are nonpeptide antigens that alone are too small to provoke an immune response. Nevertheless, T-cell responses to haptenic allergens clearly occur and are critically involved in allergic immune responses to drugs such as penicillin. Although the mechanisms that generate T-cell epitopes from protein antigens are well understood, haptens create T-cell epitopes by alternative mechanisms. These may include binding of haptens directly to preformed MHC-peptide complexes on the cell surface, or indirect association with MHC molecules after conjugation with self cell surface or serum proteins that are then processed and presented as haptenated peptide antigens. Which of these unorthodox mechanisms of epitope generation is dominant in allergy to penicillin is unknown. This study aims to determine the nature of the epitopes recognized by amoxicillin-specific T cells from allergic donors, and to clarify whether T-cell responses to penicillin antibiotics are MHC-restricted and require haptenated self proteins to be processed before recognition. Human T-cell lines specific for amoxicillin were raised and used in assays with processing-disabled and MHC-class II-typed antigen-presenting cells to determine the MHC restriction and processing requirements of T cells recognizing amoxicillin. Fixation of antigen-presenting cells with paraformaldehyde, before or after pulsing with amoxicillin, established that T cells can recognize amoxicillin-containing epitopes with a similar efficiency irrespective of whether the antigenic conjugate has been internalized and processed. These results suggest that amoxicillin can bind directly to performed MHC-peptide complexes and need not necessarily involve the processing of haptenated self carrier proteins before recognition of the conjugate by amoxicillin-specific T cells.

Blebs in the mouse cerebellar granular layer as a sign of structural inhomogeneity. 1. Anterior lobe vermis

The cerebellum is a modular structure. However, the size of the fundamental compartments is uncertain, with anatomical methods showing a parasagittal band arrangement but electrophysiological mapping suggesting a finer subdivision into microzones and patches. A new anatomical way to demonstrate compartmentation is described. The cerebellum is fixed by perfusion with 70% ethanol, paraffin-embedded and sectioned. When the sections are rehydrated the granular layer pleats into an elaborate array of blebs. These blebs are seen in both transverse and sagittal sections, found in all lobules of both the vermis and the hemispheres, symmetrical about the midline, reproducible between neighboring sections and between individuals, and bear a constant relationship to the Purkinje cell bands as revealed by zebrin II immunocytochemistry. The data suggest that the granular layer of the adult mouse cerebellum is divided into several thousand modules. These modules may reflect the mossy fiber topography, and may be the anatomical equivalents of the tactile receptive field patches. Such a profound compartmentation has important implication for theories of cerebellar structure and development.

Chemical inactivation of recombinant vaccinia viruses and the effects on antigenicity and immunogenicity of recombinant simian immunodeficiency virus envelope glycoproteins

The efficiency of paraformaldehyde (PFA) and binary ethylenimine (BEI) in inactivating recombinant vaccinia virus (rVV), present in baby hamster kidney cells expressing simian immunodeficiency virus envelope glycoproteins (SIV-Env), was measured in a series of inactivation studies. Both compounds were shown to be effective in reducing rVV titres. The use of standard 3-day titration assays proved to be inadequate to measure PFA inactivation, since upon prolonged incubation, residual rVV infectivity was detected in cultures negative at 3 days. Different procedures using PFA or BEI were selected to assess their influence on the antigenicity and immunogenicity or rVV expressed SIV-Env. Antigenicity, as defined by the ability to react with a panel of monoclonal antibodies recognizing major antigenic sites, and immunogenicity, as defined by the ability to induce SIV envelope specific and virus neutralizing serum antibodies in rats, proved to be preserved after either inactivation procedure. These data show that both protocols using PFA or BEI can be used successfully as part of the procedures to remove residual rVV infectivity.

The effect of fixation type on DNA extracted from paraffin-embedded tissue for PCR studies in dermatopathology

BACKGROUND

Amplification of nucleic acids from paraffin-embedded material by the polymerase chain reaction (PCR) is widely used to detect viral genomes, clonal gene rearrangements and oncogene mutations in skin specimens. Fixation with embedding of skin tissue is a procedure that has a profound effect on its molecular arrangement.

OBJECTIVE

The aim of this study was to determine the effect of different fixatives on the PCR amplification of DNA.

METHODS

We fixed randomly chosen fresh pathologic skin specimens in formalin, ethanol and Histochoice for 24 and 72 h and then embedded the tissue in paraffin. DNA was extracted from the paraffin-embedded tissues and used as template for amplification, producing 530- and 760-bp fragments of the phosphoglycerokinase gene.

RESULTS

Our results indicate that PCR can be performed with excellent results on ethanol- and Histochoice-fixed, paraffin-embedded skin tissue with a rate of success comparable to that using fresh tissues; formalin-fixed tissue gave slightly less satisfactory results.

CONCLUSION

This investigation corroborates previous reports investigating the effect of ethanol and formalin fixation on DNA amplification by PCR. Moreover, this is the first study showing that DNA extracted from tissue fixed with Histochoice is suitable for PCR gene amplification.

Modified formalin and methanol fixation methods for molecular biological and morphological analyses

Several simplified fixation methods were examined to determine their suitability for both molecular biological analyses and morphological study. Fixation with 10% v/v formalin alone at 4 degrees C and containing 5 mmol/L ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA) at room temperature preserved significantly more high-molecular-weight DNA than 10% v/v formalin fixation at room temperature. The morphological differences between tissues fixed using these modified formalin fixation methods and conventional 10% v/v formalin fixation were negligible. Of the dehydration fixatives tested, 100% methanol did not cause regional differences due to artificial tissue shrinkage and the morphology of sections prepared by methanol fixation was preserved consistently better than that of acetone- or ethanol-fixed sections. All three dehydration fixatives preserved relatively higher-molecular-weight DNA and RNA, compared with formalin. Cold formalin, formalin containing EDTA at room temperature and 100% methanol are recommended as standard and additional fixatives routine clinicopathological laboratory use.

High glutaraldehyde concentrations reduce rather than increase the calcification of aortic wall tissue

BACKGROUND AND AIMS OF THE STUDY

This study was performed in order to: (i) determine whether a similar reduction of tissue calcification as seen after prolonged storage can be achieved through higher concentrations of glutaraldehyde (GA); and (ii) verify that well-preserved tissue integrity can suppress calcification.

METHODS

Before fixation in 0.2% GA (PBS, 4 degrees C, seven days) porcine aortas were kept on ice for 48 h. Alternatively, tissue was immediately fixed at the abattoir in 0.2%, 1.0% or 3% glutaraldehyde (PBS, 4 degrees C, seven days). A second group of immediately fixed tissue (0.2%, 1.0%, 3.0% GA) (PBS, 4 degrees C, two days) had an interim step of L-lysine treatment (0.1M, 37 degrees C, acetic acid buffer, two days) in order to enhance cross-linking followed by warm-temperature fixation (PBS, 37 degrees C, five days). Two animal models were compared: subcutaneous implantation in rats (12 weeks) and vascular implantation in non-human primates, Chacma baboons (six weeks).

RESULTS

In both animal models the highest level of calcification was found in the group with delayed fixation in 0.2% GA. In the rat model there was an inverse correlation between tissue calcification and the GA concentration used, with 3% GA-fixed tissue showing the lowest level of tissue calcium. Overall, increasing GA concentration had a significant benefit on calcification (p < 0.0001; two-factor analysis of variance). Enhancement of cross-linking with L-lysine further abrogated tissue calcium levels at all GA concentrations (p < 0.0001; two- factor analysis of variance). Although the short-term baboon model showed lower tissue calcium levels, the trend seen in the rat model was confirmed.

CONCLUSIONS

Our results demonstrate the detrimental effect of delayed fixation and further suggest that, against previous beliefs, fixation at higher glutaraldehyde concentrations reduces the calcification tendency of cross-linked aortic tissue.

CAG repeat analyses in frozen and formalin-fixed tissues following primer extension preamplification for evaluation of mitotic instability of expanded SCA1 alleles

Neurodegenerative disorders, including spin-ocerebellar ataxias (SCA), Huntington disease (HD) and dentatorubral-pallidoluysian atrophy (DRPLA), are associated with unstable CAG repeats. To investigate the mitotic stability of the repetitive element in the genes for SCA1, SCA3, HD, and DRPLA we extracted DNA from up to 13 tissue samples from four deceased individuals with progressive neurological disorders and neuropathological signs. Due to the formalin fixation of some tissues the genomic DNA was highly degraded and unsuitable for amplification of fragments longer than 150 bp. After size selection and primer extension preamplification, specific analyses could be performed even for expanded alleles. In all four patients the SCA1 mutation could be demonstrated, in one case with remarkable somatic heterogeneity of the elongated allele, whereas alleles of the normal range were stable in all tissues examined.

Glutaraldehyde detoxification of aortic wall tissue: a promising perspective for emerging bioprosthetic valve concepts

BACKGROUND AND AIMS OF THE STUDY

Due to its superb crosslinking activity, glutaraldehyde (GA) is still the most widely used fixative for bioprosthetic heart valves. At the same time, however, GA is also believed to be partly responsible for tissue calcification and the lack of surface re-endothelialization, both of which may contribute to valve degeneration. Although excess GA has previously been extracted from thin leaflet tissue, this treatment proved insufficient for the detoxification of thick aortic wall tissue of stentless valves or root prostheses.

METHODS

In order to establish a detoxification procedure which thoroughly extracts biologically active GA from aortic wall tissue, we used a highly sensitive bioassay where endothelial cells were seeded onto glutaraldehyde-fixed aortic wall discs following various detoxification procedures. Absolute cell numbers and morphologic shape were correlated with shrinkage temperature and shrinkage extent of the tissue to determine the potential of the treatments to reverse crosslinks. To optimize treatment conditions, pH (3.2 versus 4.5), temperature (22 degrees C versus 37 degrees C) and incubation time (48 h versus one week) were varied. In order to identify an optimal detoxification agent, 12 different amino-reagents from four chemical groups were compared: low pKa aromatic amines, amino acids, low pKa N-heterocyclic compounds and amino sugars.

RESULTS

Amino-reagent treatment required warm temperature (37 degrees C), prolonged reaction time (one week) and a pH of 4.5 to achieve long-term cell growth on glutaraldehyde-fixed aortic wall. All 12 amino-reagents were able to detoxify aortic tissue satisfactorily; and all mildly reversed crosslinks, although there were differences between candidates. When summarized data were ranked correlating cell growth and quality with shrinkage temperature and shrinkage extent, seven reagents had a rank sum above the overall mean value, and five below with statistically significant differences between candidates. The additional stabilization of the detoxification reaction through borohydride-reduction had no further effect on tissue biocompatibility and crosslinks.

CONCLUSIONS

Efficient detoxification of thick aortic wall tissue is possible if a one-week incubation in an acetic acid buffer-based amino-reagent is carried out at 37 degrees C.

Improved ultrastructural preservation of bioprosthetic tissue

BACKGROUND AND AIMS OF THE STUDY

Poor ultrastructural tissue preservation of bioprosthetic heart valves is associated with a higher propensity for calcification. In spite of this realization, commercial valve fixation remains suboptimal.

METHODS

In an attempt to maintain tissue integrity through improved cross-linking procedures, transmission electron microscopy and a 21-point damage score were applied to assess the ultrastructural preservation of aortic wall tissue-the main component of contemporary aortic valve bioprostheses. An ideal glutaraldehyde (GA) concentration was assessed by immediate tissue fixation at 4 degrees C comparing 0.2%, 0.5%, 0.65%, 1.0%, 2.0%, 3.0% and 4.0% GA in phosphate-buffered saline (PBS). Subsequently, an optimal concentration of 3.0% GA was used to determine the effect of fixation temperature (4 degrees, 22 degrees and 37 degrees C). Finally, the superior glutaraldehyde concentration (3.0%) and cross-linking temperature (4 degrees C) were used to assess tolerance towards delayed fixation.

RESULTS

When different GA concentrations were used almost identical damage scores of 6.3 and 5.8 were found for 0.2% and 0.65% fixation. The first significant improvement was found at a concentration of 1.0% (score 3.3; p < 0.01) followed by a further improvement at 3.0% (score 2.6; p = 0.05). The optimal fixation temperature was 4 degrees C (3.7) with the worst results obtained at room temperature (score 9.2; p < 0.03). When fixation was delayed, the most significant damage occurred during the initial 30 min after slaughter (from 2.3 to 7.4; p < 0.02) followed by another significant deterioration between 4 and 16 h (from 5.6 to 9.7; p < 0.02).

CONCLUSIONS

In summary, the prerequisites for an ideal ultrastructural preservation of bioprosthetic aortic wall tissue are immediate fixation (within 30 min), high GA concentrations (> 1.0%) and cold-temperature fixation (4 degrees C).

[Study of physicochemical properties of lens capsule preserved under different conditions]

The role of lipid peroxidation (LPO) in the lens capsule in its preservation under different conditions is investigated. The content of LPO products (hydroperoxides and malonic dialdehyde) appreciably increased in the lens capsule after preservation in normal and Ringer's saline for 1 to 6 days at 4 degrees C. These changes were paralleled by a reliable decrease in the content of various SH groups (Superficial, structurally masked protein, and glutathion) and in catalase activity. Preservation of the lens capsule in 1% gentamicin solution almost completely prevented such changes during the first 6 days of storage. Moreover, in model systems gentamicin suppressed the intensity of Fe(2+)-ascorbate-stimulated LPO. Intensification of LPO is believed to play an appreciable role in the structural and functional disorders in the lens capsule during its storage in different media. High antioxidative activity of gentamicin recommends it as an effective preserving agent for clinical purposes.

Fixation-dependent organization of core histones following DNA fluorescent in situ hybridization

We have evaluated the effects of different DNA denaturation protocols commonly used in DNA fluorescent in situ hybridization (FISH) experiments on chromatin structure using indirect immunofluorescence. The use of antibodies to acetylated histones H3 and H4 demonstrates that the different procedures differ considerably in their extent of histone displacement. Procedures involving paraformaldehyde fixation were found to be compatible with the structural preservation of acetylated chromatin organization by indirect immunofluorescence. These results provide a basis for interpreting DNA FISH experiments aimed at determining chromatin organization of individual loci.

Sporicidal activity of chemical and physical tissue fixation methods

AIMS

The effects of alcohol based fixation and microwave stimulated alcohol fixation were investigated on spores of Bacillus stearothermophilus and Bacillus subtilis (var. niger).

METHODS

Spores were exposed to 10% formalin, or different concentrations of various alcohol containing fixatives (Kryofix/Spuitfix). Adequate controls were also set up in conjunction with the test solutions. The spores were immersed with and without adjunctive microwave stimulation in the various solutions tested. Possible surviving spores were recovered in revival broth and after incubation, and Gram staining viable counts were performed.

RESULTS

Alcohol based fixatives did not have a sporicidal effect on B stearothermophilus or B subtilis (var. niger) spores, and microwave stimulated alcohol fixation at 450 W and up to 75 degrees C did not have a sporicidal effect.

CONCLUSIONS

When alcohol based fixatives are used for fixation, precautions should be taken with the material thus treated, as it may contain viable spores or other pathogens, which are destroyed after 24 hours of formalin treatment. Of the physicochemical methods tested involving microwaving, none was successful in eliminating viable spores from the test material.

A solvent-based fixative for electron microscopy to improve retention and visualization of the intestinal mucus blanket for probiotics studies

Samples of pig small intestine, cecum, and large intestine were prepared for scanning electron microscopy (SEM), concentrating on mucus blanket retention and visualization. Samples were fixed using three aqueous-based fixatives which included a standard glutaraldehyde fixative alone as the control and the standard fixative formulation with either ruthenium red or alcian blue added and using one solvent-based fixative, osmium tetroxide dissolved in FC-72 (a degreasing fluorocarbon solvent produced by 3M Canada, Inc.), which had been successfully used by Sims et al. [(1991) Biotech. Histochem., 66:173-180] to preserve tracheal mucus of nonhuman mammals. Pig intestine samples prepared using the solvent-based fixative retained a contiguous mucus blanket, while the aqueous-based treatments retained only patchy or fibrous remnants to a degree depending on fixative composition and intestinal site. We conclude that preparation of the pig intestinal mucus layer using the solvent-based fixative suggested by Sims et al. (1991) preserves the mucus blanket in its entirety and gives superior results to aqueous-based fixatives containing the standard additives ruthenium red and alcian blue. We recommend that this anhydrous fixation, which requires only a slight modification from standard conditions, be adopted when mucus layer retention and visualization is important, as in the field of probiotics. Overcoming this major technical obstacle will now allow electron microscopy (EM) to once again provide new in situ information in this reemerging field.

Paraformaldehyde effect on ruthenium red and lysine preservation and staining of the staphylococcal glycocalyx

The utility of lysine in glutaraldehyde-ruthenium red fixatives for the preservation and/or staining of the fibrous staphylococci glycocalyx was improved by inclusion of paraformaldehyde. Short, 20 min prefixation times for paraformaldehyde-glutaraldehyde fixatives containing lysine, with or without ruthenium red, were compared to an extended overnight fixation. Samples were often lost in fixatives that did not contain paraformaldehyde at extended fixation times hampering the effective use of these fixatives for clinical or environmental applications. Inclusion of paraformaldehyde in the fixation with lysine permitted longer fixation times as well as stabilized the staphylococcal glycocalyx. Thus, the technical usefulness of fixatives employing lysine was significantly improved.

Viscoelasticity of dynamically fixed bioprosthetic valves. II. Effect of glutaraldehyde concentration

OBJECTIVE

We have previously shown the benefits of dynamic fixation over conventional static fixation of bioprosthetic valves. In an attempt to increase the durability of bioprosthetic heart valves, we explored the benefit of low-concentration glutaraldehyde dynamic fixation.

METHODS

Pig aortic valves obtained fresh from the abattoir and excised with the entire root were dynamically fixed in glutaraldehyde phosphate buffer solutions varying in concentration from 0.05% to 2.5%. Denaturation temperatures were measured and mechanical testing was performed at low (3 mm/sec) to high physiologic rates (30 mm/sec) at 37 degrees C in isotonic modified Hanks solution.

RESULTS

When fixed dynamically in 0.05% glutaraldehyde solution for 24 hours, the tissue reached a degree of cross-linking (denaturation temperature = 82.8 degrees +/- 0.6 degree C) significantly higher than that obtained for 0.05% static fixation (denaturation temperature = 79.3 degrees +/- 0.9 degree C) (p < 0.05) but similar to that for conventional static fixation in 0.5% glutaraldehyde solution (denaturation temperature = 83.5 degrees +/- 0.3 degree C). After fixation in low-concentration glutaraldehyde (0.05%), final relaxation slopes and moduli in the circumferential direction were significantly higher than those for the statically fixed tissue but similar to those for the fresh tissue. However, both dynamic and static fixation had the effect of increasing tissue extensibility to similar extents in both directions, irrespective of glutaraldehyde concentration.

CONCLUSIONS

Dynamic glutaraldehyde fixation of a porcine aortic valve at lower concentrations resulted in a better degree of cross-linking and a material with biomechanical properties that more closely mimic those of natural heart valve tissue.

Quantitative comparison of immunohistochemical staining intensity in tissues fixed in formalin and Histochoice

Formaldehyde fixatives have traditionally been used to preserve tissues as they impart excellent morphological preservation. Formaldehyde fixes tissue by cross linking, a process which can reduce the antigenicity of tissue and weakens the intensity of immunohistochemical stains. Preliminary studies have shown that Histochoice tissue fixative offers equal or greater staining intensity than neutral buffered formalin (NBF). This study compares these fixatives quantitatively and presents the results in unambiguous statistical terms. Tissue samples were collected, bisected, and fixed in NBF or Histochoice. The sections were stained with a total of 21 antibodies, and color images were collected. The hue, saturation, and value were determined for each positive pixel and an ANOVA performed. Small differences in hue were noted in 8 of 21 cases. Histochoice-fixed tissue gave a greater mean saturation than NBF with 57.1% of the antibodies tested. No significant difference in the saturation was detected in 28.6% of the cases; NBF gave higher mean saturation levels with only 14.3% of the antibodies. Histochoice-fixed tissue was found to give lower values in 66.7% of cases than those prepared with NBF, indicating darker staining. These results show that Histochoice produces staining intensity that is comparable, and in many cases superior, to formalin.

Estimation of age from teeth by amino acid racemization: influence of fixative

To determine the age of a subject from teeth accurately utilizing the racemization rates of amino acids, standard samples of the same tooth species from the same jaw are necessary as controls, as well as data for identification. However, standard teeth are generally stored in fixatives such as ethanol and formalin. We investigated and compared the degree of progression of racemization of dentinal aspartic acid in teeth stored in 95% ethanol, 10% formalin, or 10% neutral formalin fixatives. The racemization rate of dentinal aspartic acid in teeth stored in 10% neutral formalin was the highest, followed by that for teeth stored in 10% formalin then that for teeth stored in 95% ethanol. Teeth stored in these fixatives at 15 degrees C showed almost no progression of racemization. The racemization ratio (D/L ratio) in teeth extracted 10 years previously was almost unchanged from that at the time of extraction, and allowed an accurate evaluation of the subjects age at tooth extraction.

Formalin fixation strongly influences biomechanical properties of the spine

As fresh human cadaveric spine specimens for in vitro testing are hard to obtain and carry a potential risk of infection, the possibility of using embalmed spine specimens has been considered. The cross-linking effect of formalin fixation, however, raises uncertainties regarding the biomechanical likeness of preserved specimens. They have been reported to be stiffer, but no quantitative data exist. The purpose of this study was to determine the biomechanical differences between fresh and formalin-fixed spine specimens, using L1-2 motion segments from six 16-week-old calf spines. The range of motion and neutral zone were determined in flexion-/extension, left/right axial rotation, and right/left lateral bleeding. The range of motion decreased in the formalin fixed specimens by as much as 80%, and the neutral zone by as much as 96%. The results of this study therefore imply that, for biomechanical testing, formalin-fixed specimens are not representative of the in vivo conditions.

A method for co-localization of tubular lysosomes and microtubules in macrophages: fluorescence microscopy of individual cells

Routinely used procedures for chemical fixation often fail to preserve delicate membrane-bounded tubular structures in a variety of cell types. Fixation procedures commonly employed in immunocytochemical studies for localization of structural proteins, such as those found in cytoskeletal elements, may also degrade these tubular structures. Here we describe a procedure that preserves the elaborate tubular lysosome system found in stimulated macrophages and allows the subsequent immunofluorescence localization of microtubules in the same cells. Use of this methodology permits the assessment of the spatial relationship between tubular lysosomes and microtubules in macrophages.

Preservation of spatial organization and antigenicity of leukocyte surface molecules by aldehyde fixation: flow cytometry and high-resolution FESEM studies of CD62L, CD11b, and Thy-1

We used transmission and scanning electron microscopy in conjunction with immunogold labeling to study cell surface molecules for evidence of distribution-function relationships. Ascription of functional significance to surface distribution therefore requires preservation of cell morphology and maintenance of molecular expression and distribution through the multiple steps of cell preparation. These requirements prompted us to compare two methods for preparing leukocytes for analysis of surface molecule distribution: one method involved using low temperature to "stabilize" cell morphology and surface molecular organization through immunolabeling; the other involved fixation of the cells with dilute glutaraldehyde before their isolation and labeling. Binding of primary antibodies to several surface molecules, measured by flow cytometry, was comparable for cells prepared by the two methods. Cell morphology and molecular distributions, assessed by high-resolution field emission SEM, were likewise comparable. These results support the conclusion that cell morphologies and CAM distributions previously reported were not affected by exposure of the cells to low temperature through isolation and immunolabeling. Our additional observation that Thy-1 is expressed on both non-projecting and projecting membrane domains of mouse lymph node lymphocytes and rat thymocytes represents a third and new pattern of surface molecule distribution.

Rapid single-step method for flow cytometric detection of surface and intracellular antigens using whole blood

Fixation/permeabilization methods used for the detection of intracellular antigens by flow cytometry often result in the destruction of cellular morphology and surface immunoreactivity, properties useful in flow cytometry for the characterization of cells in heterogeneous populations. In addition, a majority of these methods are incompatible with whole blood and require that peripheral blood leukocytes (PBLs) be purified prior to fixation. This article describes a new technique for the rapid detection of both intracellular and cell surface antigens, while preserving cell morphology, through the use of a single-step fixation/permeabilization reagent, ORTHO PermeaFix (OPF). OPF is compatible with whole blood, allowing for the direct preparation of PBLs without prior cell separation. An additional red blood cell lysing reagent was not required because RBC lysis occurred upon resuspension of OPF-treated whole blood samples in isotonic solution. Discrimination of leukocyte populations by light scatter after OPF treatment was comparable to matched unfixed live cells. In addition, absolute lymphocyte and white blood cell (WBC) counts were not significantly affected when OPF-treated cells were compared with unfixed cells. Treatment of whole blood from 7 normal donors showed no significant difference in percentage of cells positive for CD2, CD3, CD4, CD8, CD16, or CD19 between fixed and unfixed samples when cells were stained before fixation, and no difference in CD3, CD4, CD8, CD16, or CD19 percentages when cells were stained following fixation. Monoclonal antibodies specific for intracellular antigens located at various sites within the cell were tested on fixed samples. OPF-treated peripheral blood lymphocytes showed greater than 95% reactivity for the inner mitochondrial membrane protein bcl-2, and the cytoskeletal cytoplasmic protein vimentin. TIA-1, a cytolytic granule-associated protein, showed differential reactivity within lymphocyte subsets, from a low of 8 +/- 2% in CD4+ cells to 89 +/- 6% in CD16+ cells, when whole blood from five normal donors was fixed and stained. Reh cells treated with OPF showed greater than 95% reactivity for the internuclear protein TdT. A comparison of OPF with two other fixation/permeabilization procedures, 1% paraformaldehyde followed by 45% ethanol and 0.25% paraformaldehyde followed by 0.2% Tween 20, showed that only OPF could be used both prior to or following cell surface staining with no effect on antigen detection while allowing optimal detection of all of the intracellular antigens tested.

Spermatogenesis in mosquitoes (Diptera: Culicidae)

An ultrastructural study of spermatogenesis has been carried out on 18 species of mosquitoes of the Anophelinae, Culicinae and Toxorhynchitinae sub-families. In this spermatogenesis, which follows a classical way, primordial cells, primary and secondary spermatogonia, as well as primary and secondary spermatocysts are considered. We have identified 9 stages of development all along the spermiogenesis. This process ends up with the formation of a needle-like spermatozoon showing head and tail regions. After a treatment with tannic acid, the protofilaments of the axoneme of Culex tigripes are counted. For the first time we have carried out a complete study of spermatogenesis in mosquitoes.

Ultrastructural identification of a membrane-like structure on the surface of normal articular cartilage

Cytochemical and immunocytochemical approaches have been applied to the study of the surface of articular cartilage in humans, bovine and rats. Specimens were fixed in situ or soon after bioptic sampling with chemicals able to preserve and visualize proteins (glutaraldehyde, tannic acid), lipids (osmium tetroxide, malachite green, uranyl acetate) and proteoglycans (toluidine blue O, cuprolinic blue, cetyl pyridinium chloride). Mixtures of reagents were also used. Oriented serial thin sections were observed as such or after treatment with chemicals (chloroform-methanol, Triton X 100) or enzymes (chondroitinases, hyaluronidases, trypsin). Hyaluronan was detected by the use of glial-hyaluronate-binding-protein and antibodies against it. High concentration of osmium tetroxide or fixatives containing markers for lipid or for proteoglycans revealed that the surface of the articular cartilage, in all animal species examined, was covered by mono-multilayered discontinuous three-laminar sheets, which could be partly removed by chloroform-methanol and Triton X 100, were sensitive to hyaluronidase, chondroitinase and trypsin, and were immunopositive for hyaluronan. Each three-laminar sheet was 12-14 nm thick, was always separated from the cartilage itself and could be easily displaced. It is proposed that the surface of normal articular cartilage is covered by a discontinuous mono/multilayered pseudo-membrane, that can be better preserved by fixatives injected into the joint cavity and seems to consist of phospholipids, glycosaminoglycans and proteins. This membrane-like structure might have a protecting role in preventing direct contacts between the articular cartilage and toxic agents present in the synovial fluid and/or exert a lubricating effect within the articular joint.