Mucopolysaccharides in suspensions of Treponema pallidum extracted from infected rabbit testes

Polypeptides of Treponema pallidum: progress toward understanding their structural, functional, and immunologic roles. Treponema Pallidum Polypeptide Research Group

Treponema pallidum subsp. pallidum, the spirochete that causes syphilis, is unusual in a number of respects, including its small genome size, inability to grow under standard in vitro culture conditions, microaerophilism, apparent paucity of outer membrane proteins, structurally complex periplasmic flagella, and ability to evade the host immune responses and cause disease over a period of years to decades. Many of these attributes are related ultimately to its protein content. Our knowledge of the activities, structure, and immunogenicity of its proteins has been expanded by the application of recombinant DNA, hybridoma, and structural fractionation techniques. The purpose of this monograph is to summarize and correlate this new information by using two-dimensional gel electrophoresis, monoclonal antibody reactivity, sequence data, and other properties as the bases of polypeptide identification. The protein profiles of the T. pallidum subspecies causing syphilis, yaws, and endemic syphilis are virtually indistinguishable but differ considerably from those of other treponemal species. Among the most abundant polypeptides are a group of lipoproteins of unknown function that appear to be important in the immune response during syphilitic infection. The periplasmic flagella of T. pallidum and other spirochetes are unique with regard to their protein content and ultrastructure, as well as their periplasmic location. They are composed of three core proteins (homologous to the other members of the eubacterial flagellin family) and a single, unrelated sheath protein; the functional significance of this arrangement is not understood at present. Although the bacterium contains the chaperonins GroEL and DnaK, these proteins are not under the control of the heat shock regulon as they are in most organisms. Studies of the immunogenicity of T. pallidum proteins indicate that many may be useful for immunodiagnosis and immunoprotection. Future goals in T. pallidum polypeptide research include continued elucidation of their structural locations and functional activities, identification and characterization of the low-abundance outer membrane proteins, further study of the immunoprotective and immunodiagnostic potential of T. pallidum proteins, and clarification of the roles of treponemal proteins in pathogenesis.

The importance of different components of normal human serum and lysozyme in the rapid immobilisation of purified Treponema pallidum, Nichols strain

OBJECTIVES

To study the role of different components in normal human serum and the role of lysozyme in rapid immobilisation of Percoll purified T pallidum (Nichols).

MATERIALS AND METHODS

The immobilisation of Percoll purified T pallidum was studied after pre-incubations with different serum fractions (Fr) of normal human serum (Fr 1, containing IgM; Fr 2, containing IgG and a low level of haemolytic complement, and Fr 1 (abs), depleted of IgG). A guinea-pig serum pool was used as a complement source in the immobilisation experiments. The influence was studied of removal of lysozyme from guinea-pig serum on the immobilisation reactions. Further experiments were performed, using a fluorescence technique, to detect C3b depositions on fixed treponemes and treponemes in suspension.

RESULTS

Rapid immobilisation of Percoll-purified treponemes by the NHS serum fractions occurred only after preincubation with Fr 1 and Fr 2 simultaneously. This was largely dependent on the presence of a small amount of haemolytic C in Fr 2. Removal of lysozyme reduced this rapid rate of immobilisation. In fluorescence experiments it was demonstrated that C3b deposition on fixed (that is damaged) treponemes occurred upon their incubation with Fr 2 or the combination of Fr 1 and 2. However, on treponemes in suspension C3b deposition occurred only after incubation with the combination of Fr 1 and 2.

CONCLUSION

The rapid immobilisation of Percoll purified treponemes by serum fractions from normal human serum requires antibodies of the IgM and IgG class, together with complement and lysozyme. Omission of one of these reactants slows immobilisation. Our experiments suggest that the reactants act in sequence: the loss of integrity of the outer membrane by an attack by IgM and C offers the opportunity for lysozyme to hydrolyse the peptidoglycan layer surrounding the cytoplasmic membrane of the treponemes, which then is accessible for attack by antibodies and C.

The influence of different sera on the in vitro immobilisation of Percoll purified Treponema pallidum, Nichols strain

OBJECTIVES

Investigation of sera, especially rabbit serum, in preventing in vitro immobilisation of Percoll purified T. pallidum.

MATERIALS AND METHODS

The immobilisation of Percoll purified T. pallidum (Nichols) was studied after pre-incubations with basal reduced medium (BRM), heat-inactivated serum of seven different species of animals, heat-inactivated normal human serum (NHS) and rabbit sera containing a different level of antitreponemal antibodies. Also increasing percentages of heat-inactivated normal rabbit serum (NRS) were studied.

RESULTS

The rapid immobilisation of purified treponemes by NHS is delayed by pre-incubation with NRS in a dose-dependent manner. The treponemes from 5-day infections were immobilised significantly more slowly than treponemes from 7- and 8-day infections. Compared with NRS, pre-incubations with a high-titred, low-titred and "autologous" serum resulted in significantly more rapid immobilisation of the treponemes. With most other animal sera resistance to immobilisation was slight compared with that produced by NRS. Immunofluorescent studies revealed that the treponemes were covered with a layer of the human third complement factor (C3b), within an hour of incubation. With two sequential pre-incubations, a delay of the immobilisation was only noted in those test mixtures in which NRS had been present in both preincubations.

CONCLUSION

Rabbit serum delays the rapid in vitro immobilisation of Percoll purified treponemes by normal human serum. There was no evidence that this was caused by preventing access of antibodies (in vivo as well as in vitro) to, or preventing the activation of complement on, the treponemal surface. The evidence points to a mechanism in the fluid phase, suggesting participation of a third factor in the immobilisation process, for instance an enzyme, which can be partially inhibited by rabbit serum component(s).

Rapid in vitro immobilisation of purified Treponema pallidum (Nichols strain), and protection by extraction fluids from rabbit testes

The use of Percoll-purified treponemes in an assay similar to the Treponema pallidum Immobilisation test demonstrated that immobilisation of purified treponemes by seronegative normal human serum proceeded at a much higher rate than that of unpurified treponemes. This suggests that the removal of the testicular extract makes the treponemes more vulnerable to this action. A preincubation of the purified treponemes with the testicular extract from infected or uninfected testes delayed their rate of immobilisation to that demonstrated by the unpurified treponemes. This showed that substances produced during the infection are probably not responsible for the delay in immobilisation. Discrimination between the classical and the alternative pathway of complement activation, studied by the ethylene glycol-bis (beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA) method, showed that the classical pathway was responsible for the rapid immobilisation of the purified treponemes. However, the slow immobilisation in the EGTA-serum samples suggested a minor role of the alternative pathway in the immobilisation of the purified treponemes. Since the testicular extracts exerted an anti-complement activity, it needs to be investigated whether the protection offered to the purified treponemes by the testicular extracts is based on their deteriorating effect on the classical complement pathway or is due to a re-establishment of the protective cover around the treponemes.

Serum lipoprotein binding by Treponema pallidum: possible role for proteoglycans

Acquisition by the syphilis spirochaete, Treponema pallidum, of radioiodinated total human plasma lipoprotein and lipoprotein subfractions was examined. Time dependent and saturation binding kinetics were observed for total lipoproteins and subfractions, including high density lipoproteins, low density lipoproteins (LDL), and very low density lipoproteins. All subfractions competed equally well in binding iodinated total lipoproteins and individual subfractions, but apoproteins common to all subfractions were ineffective in inhibiting lipoprotein acquisition. The interaction of LDL with T pallidum was studied further and, interestingly, the presence of 17% sulphated dextran sulphate (DS) in the reaction mixture containing treponemes and LDL resulted in up to 172 times more LDL being bound by live treponemes. Biological variability was observed in the extent of increased LDL bound in the presence of 17% sulphated DS by preparations of T pallidum isolated from different infected rabbits. Saturation kinetics of iodinated LDL acquisition was obtained in the presence of 17% sulphated DS but not 1% sulphated DS. Other proteoglycan molecules, such as chondroitin sulphate, hyaluronic acid and heparin, and fibronectin, the extracellular matrix protein targeted by treponemes in parasitism of host cells and tissues neither diminished nor enhanced LDL binding by live treponemes. Only 5% and 10% of associated radioactivity was released from treponemal surfaces after T pallidum was incubated with iodinated LDL and 17% sulphated-DS for 15 and 30 minutes, respectively. These data show binding and possible internalisation of host lipoproteins by T pallidum, which may be mediated by sulphated proteoglycan. Sulphated proteoglycans accumulate during T pallidum infections of host cells.

Light and electron microscopy of rabbit testes infected with Treponema pallidum (Nichols strain): nature of deposited mucopolysaccharides and localisation of treponemes

The mucopolysaccharide nature of the material deposited in rabbit testes infected with Treponema pallidum was confirmed by histochemical staining with alcian blue. Differential staining of mucopolysaccharides showed the presence of sulphated mucopolysaccharides as an almost constant feature, whereas in little more than half of the orchitic testes studied variable deposits of hyaluronic acid were seen. The treponemes were almost exclusively present in the areas rich in mucopolysaccharide. A combination staining with the Warthin-Starry method and alcian blue showed treponemes in close association with pre-existing fibrils and cells contained in these fibrils. The latter findings were confirmed by electron microscopy, and the fibroblasts to which treponemes adhered displayed the characteristics of activated cells. The close parallel between the histopathological changes observed here and their descriptions in published reports shows that our specific strain still behaves the same as the original Nichols pathogenic strain of T pallidum.

Characterization of the proteoglycans synthesized by rabbit testis in response to infection by Treponema pallidum

Organ cultures of syphilitic and normal rabbit testes were incubated with 35S-sulfate for labeling of proteoglycans. Syphilitic rabbit testes synthesized three macromolecular fractions (I, II, and III) which were not detected in extracts of normal uninfected tissue. The three fractions comprised a larger (approximately 10(6) mol wt) chondroitin sulfate/dermatan sulfate proteoglycan (Fraction I), a smaller (approximately 10(5) mol wt) chondroitin sulfate/dermatan sulfate proteoglycan (Fraction II), and a putative sulfated glycoprotein of Mr 40 kd (Fraction III). The glycosaminoglycan chains of both proteoglycans eluted with a Kav of 0.45 on Sepharose CL-6B, consistent with a molecular weight of 25,000. The smaller proteoglycan was not a cleavage product of the larger species. Erythromycin had no significant effect on the synthesis of any of the three macromolecules. In contrast, the synthesis of both proteoglycans was totally inhibited by a 2-hour preincubation with cycloheximide, which suggests that the constitutive "pools" of the two core proteins were small. The putative sulfated 40-kd glycoprotein was insensitive to a 2-hour preincubation with cycloheximide.