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Biomedical subjects

I Ofek

Publications and source records attributed to I Ofek.

At least 127 records · Page 7Linked to original sources
PubMed1976

Antigens of group A streptococci involved in passive hemagglutination reactions.

Antibodies to streptococcal extracellular products were detected in rabbit sera by passive hemagglutination tests as early as 1 week after intravenous injection of live group A streptococci (strain C203S). Using these antibodies in immunoadsorbent columns, we prepared an antigenic fraction from crude concentrates of streptococcal extracellular products. The specific activity of this fraction in sensitizing glutaraldehyde-treated erythrocytes for passive hemagglutination tests and in absorbing passive hemagglutination antibodies from immune sera was increased by 80-fold and at least 24-fold, respectively, as compared with crude extracellular products. The fraction has been found to contain at least three serologically active antigens, which are of considerable interest because: (i) they gave rise to early and consistent immune responses both in humans and in experimental animals; (ii) they appear so far to be produced only by beta-hemolytic streptococci; and (iii) antibodies to these antigens are present in high titers in patients with acute rheumatic fever. Our data suggest that passive hemagglutination antigens may be distinct from those extracellular enzymes and hemolysins ordinarily employed in streptococcal serological studies.

Animals↗
PubMed1975

Cell membrane-binding properties of group A streptococcal lipoteichoic acid.

Lipoteichoic acid (LTA) was extracted from group A streptococci, previously treated with hot HCl, by the phenol method. The extracted LTA was loaded on an isoelectric (IE) focusing column and two fractions were collected; one at pH 4.65 and the other at pH 2.95. Chemical analysis demonstrated that the unfractionated LTA contained alanine and glycerolphosphate at molar ratio of 1:10, and ester-linked lipids, but no detectable sugars or amino-sugars. The two IE fractions contained lipids but lacked alanine. The LTA and its IE fractions spontaneously adsorbed to human erythrocytes (sensitization) causing them to agglutinate in the presence of rabbit anti-LTA. The RBC-sensitizing and antigenic activities of IE fractions were equal to, or greater (for IE fraction at pH 4.65) than the unfractionated LTA, indicating that alanine is not involved in the sensitizing activity of LTA. Mild ammonia-hydrolysis abolished the RBC-sensitizing activity of LTA and its IE fractions. Chloroform-methanol-soluble material of the ammonia-hydrolysate lacked antigenic activity but blocked sensitization of erythrocytes by LTA. The water-soluble material of the hydrolyzed LTA retained antigenic activity, was not able to block sensitization by LTA, and its sensitizing activity was restored after esterification with fatty acids. These experiments indicate that ester-linked fatty acids (palmitic acid being the major one) are involved in the spontaneous adsorption of LTA to erythrocytes. The LTA, its lipid moiety, and anti-LTA blocked adherence of group A streptococci to human epithelial cells, suggesting that small amounts of LTA may reside on the streptococcal surface to mediate attachment and colonization of these organisms on mucosal surfaces in vivo.

Ammonia↗
PubMed1975

Human immunity to Neisseria gonorrhoeae: acquired serum opsonic antibodies.

Recent studies have demonstrated that virulent (Types 1 and 2) colonial variants of Neisseria gonorrhoeae are highly resistant to phagcytosis by normal human polymorphonuclear leukocytes. To pursue this observation, sera from prostitutes were compared with sera from Catholic nuns in terms of their ability to enhance phagocytosis of Type 1 gonococci. The phagocytic system consisted of a monolayer of normal human polymorphonuclear leukocytes and an inoculum of 107 to 108 colony-forming units of N. gonorrhoeae. In a representative test, the mean percentages of phagocytosis were: 13 nuns, 10 per cent; 32 prostitutes, 30 per cent (p less than 0.01). In a separate set of experiments, 5 (45 per cent) of 11 patients with acute gonococcal salpingitis had significant increases in serum opsonic activity between the acute and one month convalescent bleeding. A pool of prostitute sera retained detectable opsonic activity at dilutions as high as 1:320. The opsonic activity was heat-stable, demonstrable without complement, and resided in both the IgG and IgA fractions of serum. These studies demonstrate the presence of acquried opsonic antibody to N. gonorrhoeae in humans: the significance of such antibodies in proction against gonococcal disease requires further exploration.

Antibodies, Bacterial↗
PubMed1974

Evaluation of micro complement fixation tests for antibodies against group A streptococcal M and M-associated antigens in rabbit and human sera.

Variables involved in micro complement fixation (CF) tests for type-specific (TSM) and non-type-specific (NTSM) antibodies against preparations of streptococcal M protein were studied. Sera of rabbits immunized with purified M protein which contained high titers of anti-TSM and low titers of anti-NTSM antibodies reacted type specifically in the CF tests when relatively low concentrations of M protein were employed. In contrast to these artificially induced TSM antibody responses, the sera of rheumatic fever patients demonstrated elevated CF antibody titers (1:80 to 1:320) in the presence of both high and low concentrations of M antigen. The CF test cannot distinguish TSM and NTSM antibodies when the latter predominate. The CF test can be employed with confidence for the detection of NTSM antibodies, provided that the test sera are known to lack type-specific antibodies against the M protein used in the test.

Animals↗
PubMed1974

Peptic digestion of streptococcal M protein. II. Extraction of M antigen from group A streptococci with pepsin.

M protein of group A streptococci was extracted by mild peptic digestion. Optimal amounts of type-specific M protein were released after 20 min of digestion with 0.02 mg of pepsin per ml at pH 5.8. Immunological analysis revealed that, unlike conventional HCl extracts, pepsin extracts lacked the surface C carbohydrate antigen and contained less non-type-specific, heat-stable cellular antigens; they also lacked detectable heat-labile T protein. Similar to HCl extracts, however, the pepsin-extracted M protein precipitated homologous-type M antisera and inhibited type-specific opsonization of homologous group A streptococci. Furthermore, the pepsin extract was capable of inducing type-specific opsonic M antibody in rabbits. This method may provide a useful initial step in the purification of M protein by reducing contaminating antigens.

Agglutination Tests↗
PubMed1973

Evaluation of streptozyme and antistreptolysin O tests in streptococcal pyodermal nephritis.

The evaluation of the streptozyme test in sera from 34 patients with streptococcal pyodermal nephritis was studied. Ninety-seven percent of the patients developed high titers of antistreptozyme antibodies on the first bleeding after hospitalization, in contrast to only 40% of patients who developed elevated antistreptolysin O titers. The high antistreptozyme titers declined during convalescence and reached normal levels in the sixth month after onset of the disease. The most significant fall in titers occurred between 1 and 2 months from the onset of disease. The streptozyme test may be particularly helpful as a rapid screening test for antibodies in streptococcal pyodermal nephritis.

Adolescent↗
PubMed1972

Oxygen-stable hemolysins of group A streptococci. 8. Leukotoxic and antiphagocytic effects of streptolysins S and O.

Streptolysin S exists in a cell-bound form and as an extracellular complex between a nonspecific carrier (serum, serum albumin, ribonucleic acid [RNA], Triton, Tween) and a hemolytic moiety (probably a peptide) synthesized by streptococci. Although all the forms of streptolysin S, at 100 hemolytic units, killed mouse leukocyte monolayers, the time needed to kill 100% of the cells varied with the different streptolysin S preparations. Whereas 30 min was sufficient for the cell-bound hemolysin to kill all of the cells, 60 and 180 min were required when RNA streptolysin S and serum streptolysin S, respectively, were employed. Addition of 10% mouse serum to RNA streptolysin S or to cell-bound hemolysin delayed the killing of the leukocytes. The delayed killing observed with serum and albumin hemolysins is probably due to competition for the hemolytic moiety between the carrier molecules and target sites (phospholipids) upon the leukocyte membrane. Serum streptolysin S must be constantly incubated with the cells for 90 min for 100% of the cells to undergo cytopathic changes upon subsequent incubation for an additional 90 min. Streptolysin S inhibitor (trypan blue) added to the system after 30 or 60 min of incubation resulted in the killing of 50 and 100% of the leukocytes, respectively, when the cells were further incubated for 120 min. It is suggested that 30 min of incubation was not sufficient for the transfer of enough streptolysin S molecules upon the cell surface to allow killing of all of the cells. Sublethal amounts of streptolysin S, streptolysin O, and saponin suppressed phagocytosis of streptococci by mouse peritoneal macrophages. This effect was abolished by inhibitors of streptolysin S (trypan blue) and of streptolysin O and saponin (cholesterol). With sublethal amounts of streptolysin S, no inhibition of the reduction of nitro blue tetrazolium by nonphagocytosing cells was observed, but these amounts of streptolysin S caused a 50% inhibition of the reduction of nitro blue tetrazolium by phagocytosing leukocytes. It is suggested that some metabolic systems, which are normally enhanced during phagocytosis, have been affected by sublethal doses of streptolysin S. The results indicate that the in vivo production of small amounts of streptolysins S and O by group A streptococci may inhibit phagocytosis and may thus contribute to the invasiveness and pathogenicity of this microorganism.

Animals↗