BACTERIOSTATIC EFFECT OF HUMAN SERA ON GROUP A STREPTOCOCCI : I. TYPE-SPECIFIC ANTIBODIES IN SERA OF PATIENTS CONVALESCING FROM GROUP A STREPTOCOCCAL PHARYNGITIS

Disruption of IL-17-mediated immunosurveillance in the respiratory mucosa results in invasive Streptococcus pyogenes infection

Introduction

Streptococcus pyogenes is a Gram-positive pathogen that causes a significant global burden of skin pyoderma and pharyngitis. In some cases, infection can lead to severe invasive streptococcal diseases. Previous studies have shown that IL-17 deficiency in mice (IL-17-/-) can reduce S. pyogenes clearance from the mucosal surfaces. However, the effect of IL-17 on the development of severe invasive streptococcal disease has not yet been assessed.

Methods

Here, we modeled single or repeated non-lethal intranasal (IN) S. pyogenes M1 strain infections in immunocompetent and IL-17-/- mice to assess bacterial colonization following a final IN or skin challenge.

Results

Immunocompetent mice that received a single S. pyogenes infection showed long-lasting immunity to subsequent IN infection, and no bacteria were detected in the lymph nodes or spleens. However, in the absence of IL-17, a single IN infection resulted in dissemination of S. pyogenes to the lymphoid organs, which was accentuated by repeated IN infections. In contrast to what was observed in the respiratory mucosa, skin immunity did not correlate with the systemic levels of IL-17. Instead, it was found to be associated with the activation of germinal center responses and accumulation of neutrophils in the spleen.

Discussion

Our results demonstrated that IL-17 plays a critical role in preventing invasive disease following S. pyogenes infection of the respiratory tract.

Contribution of cryptic epitopes in designing a group A streptococcal vaccine

A successful vaccine needs to target multiple strains of an organism. Streptococcus pyogenes is an organism that utilizes antigenic strain variation as a successful defence mechanism to circumvent the host immune response. Despite numerous efforts, there is currently no vaccine available for this organism. Here we review and discuss the significant obstacles to vaccine development, with a focus on how cryptic epitopes may provide a strategy to circumvent the obstacles of antigenic variation.

Streptococcal Immunity Is Constrained by Lack of Immunological Memory following a Single Episode of Pyoderma

The immunobiology underlying the slow acquisition of skin immunity to group A streptococci (GAS), is not understood, but attributed to specific virulence factors impeding innate immunity and significant antigenic diversity of the type-specific M-protein, hindering acquired immunity. We used a number of epidemiologically distinct GAS strains to model the development of acquired immunity. We show that infection leads to antibody responses to the serotype-specific determinants on the M-protein and profound protective immunity; however, memory B cells do not develop and immunity is rapidly lost. Furthermore, antibodies do not develop to a conserved M-protein epitope that is able to induce immunity following vaccination. However, if re-infected with the same strain within three weeks, enduring immunity and memory B-cells (MBCs) to type-specific epitopes do develop. Such MBCs can adoptively transfer protection to naïve recipients. Thus, highly protective M-protein-specific MBCs may never develop following a single episode of pyoderma, contributing to the slow acquisition of immunity and to streptococcal endemicity in at-risk populations.

GAS skin infections pose a significant health problem in the tropics. They are highly prevalent in developing countries as well as amongst the Indigenous populations of developed countries. In at-risk impoverished communities the epidemiology of GAS infections is very dynamic, leading to very high rates of streptococcal-associated serious pathology including rheumatic heart disease, glomerulonephritis and invasive GAS disease. Immunity to GAS takes over 20 years to develop and this has been attributed to sequence diversity of the type-specific surface M-protein. There are more than 250 different strains of GAS and it known that antibodies to the amino-terminal segment of the M-protein can kill organisms in a strain-specific manner in vitro. In the present study, using four different strains of GAS isolated from the skin lesions of Aboriginal patients in the Northern Territory of Australia, we make the discovery that skin infection does not induce long-lived type-specific immunity. However, following reinfection with the same strain memory B cells are generated and long-term strain-protective immunity then develops. The dependence on reinfection for the development of strain-specific immunity compounds with antigenic diversity of the M-protein and provides a rational explanation for the very slow acquisition of streptococcal immunity.

THE PROPERTIES OF T ANTIGENS EXTRACTED FROM GROUP A HEMOLYTIC STREPTOCOCCI

1. T antigens of group A hemolytic streptococci have been obtained in soluble form by digestion of the bacterial cells with pepsin or trypsin. Large quantities of this antigen were readily extracted from type 1 strains, whereas only small amounts could be obtained from strains of other types. 2. The T antigen, prepared in this way from a type 1 strain, was partially purified by chemical precipitation and further enzymatic digestion. An active fraction, apparently protein in nature, was separated electrophoretically at pH 7.00. The separated material, pooled and analyzed at the same pH, gave only a single peak. The isoelectric point of this substance was about pH 4.50. An elementary analysis was obtained. Although the T antigen was resistant to digestion with proteolytic enzymes and ribonuclease, it was readily inactivated by heat, especially in acid media and in strong salt solutions. The serological activity of this purified T substance was lost after exposure to ultraviolet radiation. 3. Analysis by means of the ultracentrifuge showed that the material was polydisperse and therefore probably impure. 4. The soluble form of the T substance was active in the precipitin reaction, in the fixation of complement, in inhibition of T agglutination, and as an antigen when injected into rabbits. The antibodies produced did not protect mice against infection with virulent strains of hemolytic streptococci containing the same T antigen. 5. The immunological specificity of T antigen in soluble form is the same as that of the T antigen in the intact streptococcus from which it was derived.

THE EFFECT OF TUBERCLE BACILLI ON THE POLYMORPHONUCLEAR LEUCOCYTES OF NORMAL ANIMALS

A description is given of a slide cell whereby the rate of migration of very small amounts of leucocytes can be followed and measured. The migration of polymorphonuclear leucocytes was found to be inhibited by virulent tubercle bacilli pathogenic for the class of animal (mammal or bird) from which the leucocytes were obtained; it was not affected by the avirulent variants of these microorganisms, or by bacilli pathogenic for animals of the other class. Tests failed to disclose that the inhibition of leucocytic migration resulted from any gross damage caused by the bacilli to the leucocytes.

BACTERIOSTATIC EFFECT OF HUMAN SERA ON GROUP A STREPTOCOCCI : II. COMPARATIVE BACTERIOSTATIC EFFECT OF NORMAL WHOLE BLOOD FROM DIFFERENT ANIMAL SPECIES IN THE PRESENCE OF HUMAN CONVALESCENT SERA

1. Heparin was more satisfactory for preventing blood from clotting than defibrination, potassium and ammonium oxalate, or sodium citrate in bacteriostasis of group A streptococci in the presence of streptococcal antibodies in convalescent serum. 2. Blood from rabbit, guinea pig, or sheep could not be substituted for human blood in promoting bacteriostasis when human antibody was used. Mixtures of human leukocytes and plasma of each of these animals or of animal leukocytes and human plasma were also not effective with human antibody. 3. Complement, leukocytes, and a thermostable factor which was found in human plasma were essential in the indirect bacteriostatic technique employed for the inhibition of streptococcal growth in the presence of convalescent human serum. 4. The thermostable component was active in human serum, as well as in plasma, in 1:12 dilution, withstood storage at 4° C. for at least 7 weeks, and was destroyed by heating at 70° C. for 30 minutes.

BACTERIOSTATIC EFFECT OF HUMAN SERA ON GROUP A STREPTOCOCCI : III. INTERFERENCE WITH BACTERIOSTATIC ACTIVITY BY BLOCKAGE OF THE LEUKOCYTES

1. Type-specific M extracts and group-specific C carbohydrate of group A streptococci inhibited bacteriostasis of these microorganisms in the presence of normal whole blood and of sera from patients convalescent from streptococcal infections. The inhibition was not specific with respect to streptococcal types and depended merely on the formation of precipitates in the system. The extracts had no antagonistic action in themselves. 2. Preformed precipitates derived from the interaction of an antigen and its homologous antibody or from finely divided coagulated particles of human plasma or ascitic fluid also interfered with the bacteriostasis. The supernatant fluid in which one of these precipitates was formed did not inhibit bacteriostatic activity; therefore, it seems that other possible products of the antigen-antibody reaction were not inhibitory. The relative size of the precipitate particles was a conditioning factor since small particles of one precipitate inhibited bacteriostasis, but large ones of the same precipitate failed to do so. 3. Stained films of blood cells treated with antigen-antibody mixtures which formed a precipitate revealed large cytoplasmic vacuoles containing precipitates in the polymorphonuclear leukocytes and monocytes; such engorged cells subsequently failed to phagocytize streptococci in homologous serum. Blood cells treated in the same manner, except that the antigen-antibody mixtures formed no precipitate, contained no vacuoles, and these cells were able to phagocytize the streptococci. 4. Leukocytes studied in the living state in the presence of colored precipitate and streptococci sensitized by convalescent human serum showed unselective phagocytosis of both precipitate and bacteria. The capacity of these leukocytes to ingest material however was limited. 5. As a result of non-selective saturation of their phagocytic capacity in the bacteriostatic systems containing both streptococci and precipitate, the limited number of leukocytes phagocytized only a fraction of the streptococci; consequently the remainder were able to multiply.

Variation occurring in group A streptococci during human infection; progressive loss of M substance correlated with increasing susceptibility to bacteriostasis

A study was made of the variation occurring in group A streptococci during the natural course of infection in man. From 54 patients with 56 different group A streptococcal infections of the upper respiratory tract, 251 strains of streptococci, isolated at weekly intervals following infection, were tested for their capacity to resist the bacteriostatic action of normal human blood. In 52 of the infections the streptococci were of recognized serological types and were also tested for variation in their ability to produce the type-specific M protein antigen. Strains isolated in the 1st week of infection were uniformly highly resistant to bacteriostasis and elaborated large amounts of M substance. In 42 per cent of the 52 infections, strains isolated in the convalescent and carrier stages showed an increasing susceptibility to bacteriostasis correlated with a progressive loss of M substance; whereas in the remaining 58 per cent resistance to bacteriostasis and the capacity to produce M protein were maintained throughout the observation period. In 3 different infections, the streptococci became so degraded that no M protein could be demonstrated in acid extracts of these variants. Concomitantly these strains became highly susceptible to bacteriostasis. Spontaneous reversion did not occur, but serial mouse passage reestablished these functions. These degraded variants had the same T antigen as their respective original strains. No evidence was obtained that variation of group A streptococci in resistance to bacteriostasis or in the ability to produce the type-specific M antigen was associated (a) with the appearance of type-specific bacteriostatic antibodies; (b) with any particular serological type of streptococcus; (c) with the production of streptococcal proteinase which digests the M protein; (d) with the therapeutic administration of sulfadiazine; or (e) with the development of complications. The possible relationship of these observations to the problem of the "dangerous carrier" of group A hemolytic streptococci is discussed.

The equine immune response to Streptococcus equi subspecies zooepidemicus during uterine infection

The purpose of this study was to describe strain-specific immune responses to Streptococcus equi subspecies zooepidemicus (S. zooepidemicus) during uterine infection in horses. Five isolates of S. zooepidemicus were differentiated into four strains antigenically by bactericidal testing in blood of 12 horses, and genetically by pulsed-field gel electrophoresis. Eight healthy mares were then divided into two groups, each inoculated with one strain intrauterinely on three successive oestrous cycles followed by a second strain for three successive cycles, first and second strains being reversed for each group. Immune responses to both strains were assessed by bactericidal testing and immunoblotting over eight cycles. Both techniques indicated that immune responses to each strain arose at different times. Immunoblots showed greater binding to the first inoculated strain than to the second (P < 0.05). These data confirm that immune responses to S. zooepidemicus during uterine infection are partly strain-specific.

Persistence of type-specific antibodies in man following infection with group A streptococci

Whole blood or sera were collected from individuals who had had infections with Group A streptococci of known serological type as long ago as 10 to 32 years. Most of these patients had not been treated with chemotherapeutic drugs. By means of bactericidal tests with all these sera, and mouse protection tests with some, type-specific antibodies could be demonstrated in at least half of them after a lapse of many years, the longest interval being 32 years. Two biological methods for estimating the amount of M antigen produced by Group A streptococci are described. By selecting strains for use by these methods, optimal proportions of M antigen and antibody could be employed in the tests and small amounts of antibody were, therefore, demonstrable. The assay methods for M antigen are also of value for other experimental purposes.

Transmission of group A streptococci. III. The effect of drying on the infectivity of the organism for man

The sources of airborne bacteria within living quarters are minute droplet nuclei which remain suspended in the air following expulsion from a carrier and contaminated particles which have become suspended from dried environmental deposits. Since group A streptococci may be isolated from environmental deposits in populations experiencing an epidemic of streptococcal respiratory disease (Loosli, Lemon, Wise & Robertson, 1952), it has been assumed that contaminated particles of dust serve as an important reservoir of infection. Indeed, many of our measures employed to control respiratory infection in recent years have been directed against this reservoir.

The occurrence of two M antigens in certain group A streptococci related to type 14

A strain of Group A streptococcus previously considered to belong to Type 14 was shown to have two immunologically distinct M antigens, designated Type 14 and Type 51. Most strains having the Type 14 M antigen were found to have also the Type 51 M antigen, and are considered to belong to Type 14–51. Four strains had the Type 51 M antigen without the Type 14 M antigen and one strain had the Type 14 M antigen without the Type 51 M antigen. The failure of a variant to produce the known M antigen of the parent strain does not necessarily mean that the strain is M^-, because a second M antigen may be present as was the case in several strains described here.

Evaluation of the "long chain reaction" as a means for detecting type-specific antibody to group a streptococci in human sera

Certain strains of Group A streptococci showed striking increase in chain length when grown in liquid media to which was added human sera that contained antibody to M protein of homologous type. This "long chain reaction" was shown to be a highly specific and sensitive biological test for human type-specific antibody and correlated closely with the classical bactericidal test. Patients infected with Type 12 or Type 3 Group A streptococci showed the appearance of anti-M antibody in their sera by both methods at similar intervals during convalescence. Of 217 sera studied in these patients the two tests showed agreement in all but 11 specimens. Of 99 patients who were bled serially following Type 12 or Type 3 infections, and whose sera were tested by both methods, there was close agreement, the bactericidal test being only slightly more sensitive. The advantages and limitations of this new biological test for human type-specific immunity are discussed.

Factors affecting the chain length of group A streptococci. I. Demonstration of a metabolically active chain-splitting system

Group A streptococci which grew in long chains in the presence of homologous anti-M antibody were split into their original length by the addition of an excess of homologous M protein to the culture. The chain-splitting reaction showed temperature and pH optima (37°C., 7.5) and was completely inhibited at 0°C. or by heat-killing the long chains at 56°C. prior to the addition of M protein. Addition of sublethal doses of HgCl₂, or of penicillin, inhibited the chain-splitting reaction. Pneumococci behaved in entirely comparable fashion to streptococci in similar experiments. Virulent strains of streptococci formed the shortest chains when broth media was enriched with serum. The chain-shortening effect of serum enrichment of the media was most apparent with encapsulated strains and under cultural conditions that favored capsule formation. Loss of capsules by mutation or by unfavorable growth conditions resulted in increase in chain length. The activity of the chain-splitting mechanism seemed to be independent of M protein, however, since encapsulated M-negative variants also formed very short chain in serum-enriched media. The physical presence of the capsule was not essential for chain shortening since enzymatic removal of the capsule with hyaluronidase during growth did not affect chain length. These results strongly suggest that chain-splitting of streptococci and pneumococci occurs by an active metabolic mechanism, presumably enzymatic, which is inhibited by the union of surface antigens with specific antibody.

Preparation and antigenicity of M protein released from group A, type 1 streptococcal cell walls by phage-associated lysin

The lysis of Group A type 1 streptococcal cell walls by phage-associated lysin has been described. In the preparation of lysin, a new semisynthetic non-protein media to support growth of the propagating strain of Group C streptococci was employed. Following lysis of the cell walls, the resulting digest was partially purified by ion-exchange chromatography and ammonium sulfate precipitation. In addition to M protein, the resulting preparation (called lysin M protein) contained the group-specific carbohydrate and the T protein—but did not contain antigens, detectable by precipitin tests, which cross-reacted with absorbed heterologous group or type antisera. Capillary precipitin reactions between the lysin M protein and type-specific antiserum did not occur in the presence of high ionic strength buffers; these buffers did not similarly affect precipitin reactions of acid M protein. Type 1 lysin M protein is shown to be a good antigen. A total of 1.5 mg. injected intradermally in saline produced bactericidal antibody in eight of nine rabbits; when injected in adjuvant in one rabbit, protective serum antibodies developed. Streptococci grown in sera from seven of nine rabbits immunized with lysin M protein demonstrated significantly longer chains than when grown in normal rabbit serum. Antibody as demonstrated by each of these three tests was shown to be type-specific. No local or systemic toxicity was noted following intradermal injection in rabbits of lysin M protein.

Factors involved in the induction of non-specific resistance to streptococcal infection in mice by endotoxin

Endotoxins derived from several species of Gram-negative bacteria, while inducing non-specific resistance to typhoid bacilli in mice, failed to increase the resistance of these animals to infection with virulent strains of Group A streptococci. However, if administration of endotoxin was followed by injection of minute amounts of type-specific antiserum, a substantial degree of protection against the streptococcal pathogen was obtained. The same amount of type-specific antiserum given to the animals by itself did not have any effect on the outcome of the streptococcal infection. Fresh rabbit blood, obtained from animals pretreated with endotoxin, together with anti-M protein immune serum, was found strongly bactericidal for streptococci. These observations suggest that, at least with regard to streptococcal infection, both humoral and cellular factors are required for induction of non-specific resistance.

Cross-reactivity between streptococcal M surface antigen and human skin

Psoriasis can be triggered by haemolytic streptococcal infections. As M protein is a major pathogenic surface antigen in these streptococci, the cross-reactivity between streptococcal M protein surface antigens and human epidermis was investigated. The conserved component common to the few M proteins investigated consists of an alpha-helical 'coiled-coil' configuration, similar to sub-units of human keratin. The amino acid sequence of protein M6, one of the M proteins that has been fully sequenced, was compared with that of 4721 ubiquitous peptides, by computer-assisted analysis using a protein-sequence data bank. Of all human proteins in the data bank 50-kDa keratin type 1 showed the closest homology with protein M6. Further evaluation revealed that this homology mainly involved the heptapeptide repeat patterns, which form the alpha-helical 'coiled-coil' structure, in both M6 and 50-kDa keratin. Cryostat sections of normal, involved and uninvolved psoriatic skin were studied for cross-reactivity with rabbit antisera raised against 10 different M proteins. All these antisera reacted with the stratum corneum of normal and psoriatic epidermis to a variable extent. Staining of keratinocyte cytoplasm was also observed, but this tended to be more prominent in lesional than in uninvolved and normal skin. Some of the M antisera also stained dendritic cells in the upper dermis as well as endothelium and smooth muscle. These cross-reactivities might be relevant to the pathogenesis of post-streptococcal psoriasis.

Streptococcal M protein: molecular design and biological behavior

M protein is a major virulence determinant for the group A streptococcus by virtue of its ability to allow the organism to resist phagocytosis. Common in eucaryotes, the fibrillar coiled-coil design for the M molecule may prove to be a common motif for surface proteins in gram-positive organisms. This type of structure offers the organism several distinct advantages, ranging from antigenic variation to multiple functional domains. The close resemblance of this molecular design to that of certain mammalian proteins could help explain on a molecular level the formation of epitopes responsible for serological cross-reactions between microbial and mammalian proteins. Many of the approaches described in the elucidation of the M-protein structure may be applied for characterizing similar molecules in other microbial systems.

Tropical acute rheumatic fever and associated streptococcal infections compared with concurrent acute glomerulonephritis

Ninety-three patients with acute rheumatic fever and 195 patients with acute glomerulonephritis were observed in Trinidad during an outbreak of scabies with a high incidence of secondary streptococcal infections. Clinical and laboratory manifestations of ARF were the same as those seen in temperate zones, except that antistreptolysin O titers were less markedly increased. The patients with ARF were similar to those with AGN in respect to sex, race, location of residence, and living conditions, but were older and had markedly fewer skin infections. Currently prevalent nephritogenic streptococcal strains never were isolated from patients with ARF even when M55 streptococci appeared and led to an epidemic of AGN.

Dynamics in development of experimental streptococcal immunity in mice

The interrelation between the humoral and cellular factors in the development of immunity to experimental streptococcal infection was investigated. Early resistance to infection was caused by stimulating the phagocytic cells to function efficiently in the absence of opsonins. Subsequently, the appearance of cytophilic antibodies provided further means for elimination of streptococci. Thus, in the early stages of specific antistreptococcal immunity, resistance was observed in the absence of circulating anti-M antibodies. The type-specific antibodies that appeared in the later stage did not seem to improve clearance of streptococci in the splanchnic tissues. After an intravenous lethal challenge of mice with virulent streptococci, these antibodies did not provide increased protection. The circulating anti-M antibodies were shown to play a beneficial, indeed, a crucial, role when the infection occurred in a region in which the phagocytic cells were present in a rather limited number.

EFFECT OF SUBLETHAL CONCENTRATIONS OF PENICILLIN ON THE VIRULENCE AND ANTIGENIC COMPOSITION OF GROUP A STREPTOCOCCI

Michael, J. Gabriel (House of the Good Samaritan, Children's Hospital Medical Center, Boston, Mass.), Benedict F. Massell, and Robert E. Perkins . Effect of sublethal concentrations of penicillin on the virulence and antigenic composition of group A streptococci. J. Bacteriol. 85: 1280–1287. 1963.—Virulent strains of group A streptococci were grown in sublethal concentrations of penicillin and tested for possible changes in colonial morphology, virulence, and antigenic composition. After overnight growth in broth containing penicillin, there was a marked reduction in precipitable group A and M protein content of the bacteria. Upon transfer to broth without antibiotic, the streptococci regained their ability to produce these substances. After multiple transfers in broth containing non-bactericidal levels of penicillin, variants developed which lacked group and type substances and which were also relatively resistant to penicillin. These variants were avirulent for mice and susceptible to the bactericidal action of normal human blood. Two of three strains tested, when grown on blood agar, failed to produce beta hemolysis. The mutants produced by multiple transfers in broth containing small amounts of penicillin, when passed through mice, regained all of their original properties.

LOCALIZATION OF STREPTOCOCCAL ANTIGENS IN TISSUES

A method has been described for the detection of streptococcal antigens in tissues using the indirect immunofluorescent technique. This method has been applied to the histologic distribution in the mouse of M protein of types 1, 5, 12, and 19. Histologic localization of these M proteins was similar, and their rates of disappearance from the tissues were comparable. The major sites of deposition were the endocardium and adjacent subendocardium of the heart, alveolar walls of the lung, glomerular tufts of the kidney, and reticulo-endothelial cells of liver, spleen, lymph nodes, and adrenal gland. M protein was distributed in considerably lesser concentration in capillary endothelium and connective tissue sites in myocardium, kidney, skin, and gastrointestinal tract. Traces were also present in adrenal cortical cells. It was observed only rarely in cell nuclei. After injection of 0.5 mg. M protein fraction, the concentration of antigen diminished to undetectable levels in all organ sites by 4 days, except in the renal glomerulus, where traces were visible at 8 days. In mice injected with streptococcal culture intraperitoneally, M protein was detected at sites of focal abscesses in liver and spleen, and on the serous surfaces of these organs. The histologic distribution of M protein is compared with that described previously for pneumococcal polysaccharide and animal protein. Differences in the extent of distribution and in the characteristics of antigen deposition are pointed out.

Differentiation of group A streptococci with a common R antigen into three serological types, with special reference to the bactericidal test

In further study of streptococci having the R antigen, the bactericidal test has been used instead of the mouse protection test in investigating the type-specific M antigens of these organisms. The results have been confirmed by M anti-M precipitin tests, and a correlation between the M and T antigens of the strains has been shown. On the basis of a specific M antigen, type 28 has been shown to comprise Griffith's strain Small and four other R-containing strains. A number of other strains previously thought to belong to type 28 on the basis of R antigen reactions have now been identified as belonging either to type 2 or to a new type, designated 48, which shows a one-way cross-relationship to type 13. The bactericidal test is suggested as a useful method for assessing M antigen in group A streptococci and for establishing type-specificity by means of a biological test which is more widely applicable than the standard mouse protection test.

Long chain formation by strains of group A streptococci in the presence of homologous antiserum: a type-specific reaction

Strains of group A streptococci, types 30 and 12, were observed to grow in extremely long chains in liquid media to which homologous antiserum was added. Addition to the media of antisera to heterologous types of streptococci failed to produce long chain growth. The long chain effect was destroyed by absorption of the antiserum with organisms of homologous type but was unaffected by absorption with organisms of heterologous types. The reaction disappeared at concentrations of antisera smaller than 0.25 per cent and was independent of complement or other heat-labile serum factors. Addition of trypsin to the culture to remove M protein from cells prevented long chain formation. The long chain effect depended upon the constant presence of antibody to the media. In its absence, the organisms promptly reverted to short chain growth. The phenomenon appears to have general applicability to those strains rich in M protein with only an occasional strain not responding as described. Further studies are in progress to determine the cause of this atypical response. The applicability of this phenomenon in detecting type-specific antibody using indicator strains of a variety of streptococcal types is discussed.

The ability of group A streptococci killed by heat or mercury arc irradiation to resist ingestion by phagocytes

Living group A streptococci which resist ingestion by human neutrophils in an in vitro test still do so after they have been killed by exposure to heat or to mercury are irradiation.