STUDIES ON THE MECHANISM OF RECOVERY IN PNEUMONIA DUE TO FRIEDLADER'S BACILLUS : III. THE ROLE OF "SURFACE PHAGOCYTOSIS" IN THE DESTRUCTION OF THE MICROORGANISMS IN THE LUNG

STUDIES ON THE MECHANISM OF RECOVERY IN PNEUMONIA DUE TO FRIEDLANDER'S BACILLUS : I. THE PATHOGENESIS OF EXPERIMENTAL FRIEDLANDER'S BACILLUS PNEUMONIA

Experimental pneumonia due to Friedländer's bacillus was produced in white rats by the intrabronchial inoculation of the bacilli suspended in mucin. The pneumonia was lobar in type, was almost uniformly fatal, and simulated the acute form of the natural disease in human beings. The pathogenesis of the pneumonic lesion was studied by examination of microscopic sections of the lungs of animals killed at frequent intervals during the course of the infection. The histologic characteristics of the various stages of the pneumonia were essentially the same as those previously described in experimental pneumococcal (Type I) pneumonia except for the following differences: (1) In isolated areas of the lung in Friedländer's pneumonia many more bacteria were encountered in the alveoli than were ever noted in experimental pneumococcal pneumonia. (2) Abscess formation was common in the late stages of Friedländer's infection, whereas it was not noted in the pneumococcal lesion. (3) Organization of the alveolar exudate, rarely observed in experimental pneumococcal pneumonia, was a prominent feature of the pneumonia due to Friedländer's bacillus. The mechanism of spread of Friedländer's lesion appeared to be the same as that of pneumococcal pneumonia. Likewise there was noted the same phagocytosis of organisms in the lungs of even bacteremic animals dying of the infection.

The inhibition of surface phagocytosis by the capsular slime layer of pneumococcus type III

Five strains of type III pneumococcus have been shown to possess wide capsular slime layers during the logarithmic phase of growth in serum broth. The slime layer stains metachromatically with methylene blue and can be visualized under the electron microscope as a fuzzy halo which extends well beyond the surace of the capsule proper and causes centrifugates of the organism to be of extremely large volume. This outer capsular structure is most readily demonstrated in vivo and in nutrient broth containing glucose and serum. It disappears from the surface of the cell with aging of the culture, and is easily removed by dilute alkali, alcohol, and heat. Exposure of slime-covered type III pneumococci to homologous antibody and to type III polysaccharidase reveals that the slime layer contains the same type-specific polysaccharide that is present in the rest of the capsule. From a type III strain producing a prominent slime layer an intermediate mutant has been isolated which forms small non-mucoid colonies on blood agar and possesses a relatively small capsule with a barely discernible slime layer. The wide slime layer protects virulent type III pneumococci from surface phagocytosis. Whenever the type III cells lose their broad slime layer, whether from aging of the culture, from mutation, from exposure to injurious chemicals, or from the action of type III polysaccharidase, they become susceptible to phagocytosis by the surface mechanism. Once phagocyted the type III pneumococci are promptly destroyed, even in the absence of antibodies.

Cellular mechanisms of antibacterial defense in lymph nodes; pathogenesis of acute bacterial lymphadenitis

Acute pneumococcic lymphadenitis produced in rats by intradermal inoculation of the foot-pad is characterized by rapid infiltration of polymorphonuclear leucocytes into the intermediary sinuses of the node, and prompt phagocytosis of pneumococci by both the macrophages of the sinuses and the recently arrived leucocytes. After 5 to 7 hours the polymorphonuclear leucocytes are found densely congregated about the hilar region, and 9 hours after inoculation most of the phagocyted organisms have been digested. At the end of the 24 hour period the popliteal node presents the picture of a subsiding inflammation with a marked macrophage reaction and regenerating lymph follicles. Phagocytosis of encapsulated pneumococci in the foot-pad and popliteal node occurs in less than 30 minutes after inoculation. It is assumed that this prompt phagocytosis is effected by the non-antibody mechanism of "surface phagocytosis." The majority of polymorphonuclear leucocytes that enter the sinuses of the inflamed node appear to come from capillaries within the node itself rather than from the primary site of inflammation in the foot-pad. The prompt inflammatory response of the nodal tissues serves as an active defense against lymph-borne infection. Macrophages invade nodal sinuses only after most of the pneumococci have been destroyed by polymorphonuclear leucocytes. It is suggested that the macrophage reaction follows removal of the primary inflammatory stimulus by the granulocytes, and thus constitutes only a late phase of recovery. Fibrin formation in the sinuses of the lymph node is rare during acute lymphadenitis. This finding may be related to the observation that within 5 minutes after entrance of bacteria into the node, heparin-containing granules from mast cells are strewn throughout the sinuses.

Host-parasite relationships in experimental pneumonia due to pneumococcus type III

Experimental pneumonia was produced with a highly virulent strain of type III pneumococcus which synthesizes, during rapid growth, large amounts of capsular polysaccharide. The type III pneumonia differed from that caused by pneumococcus I in that (a) death occurred more promptly in the type III infection, (b) the local pulmonary lesion became more heavily infected, and (c) frank suppuration was common even after otherwise effective chemotherapy. The greater pathogenicity of the type III organism was shown by special histologic techniques to be due primarily to its capsular slime layer which interferes with surface phagocytosis. Capsular polysaccharide shed from the organism during growth was also demonstrated in high concentration in certain parts of the pneumonic lesion. Removal of the excess polysaccharide from the alveoli resulted from (a) lymphatic drainage to regional lymph nodes and (b) phagocytosis, particularly by macrophages. The possible relationship of the free carbohydrate to the malignancy and the characteristically viscous exudate of type III pneumonia was discussed. The lung abscesses which resulted from type III infection were observed to occur in those areas in which the maximum number of organisms had accumulated. Evidence was obtained that suppuration was due, not to necrotoxic products peculiar to the type III pneumococcus, but rather to the survival of large numbers of bacteria in the tissues, brought about primarily by the antiphagocytic effect of the slime layer. When pneumonia was produced with an intermediate type III mutant lacking the protective slime layer, back mutation to the mucoid parent occurred during the course of the infection, and the mucoid form eventually predominated in the lung as a result of selective phagocytosis of the intermediate organisms. Similar mutation to the maximally virulent type III form was noted with a transformed intermediate type III strain grown from single cell preparations.

The survival of staphylococci within human leukocytes

In a study of the phagocytosis of staphylococci by human leukocytes it has been observed that strains of staphylococci producing human infection were phagocytized by human polymorphonuclear leukocytes in vitro under conditions in which virulent pneumococci, streptococci, or Klebsiella were rarely engulfed. In the presence of human leukocytes in plasma there was a rapid fall in the numbers of viable staphylococci of both pathogenic and non-pathogenic strains, the beginning of which was detectable in 10 to 15 minutes. The fall in culturable pathogenic microorganisms was considerably less marked, however, and a rapid resurgence of growth occurred in 4 to 8 hours, whereas the number of culturable non-pathogenic microorganisms remained low for 18 to 24 hours. These differences appear to be explained by the observation that a significant number of microorganisms of pathogenic strains were able to survive within human leukocytes. Such intracellular survival was found to be associated with evidence of destruction of the leukocytes. In contrast, non-pathogenic strains of staphylococci failed to survive within human polymorphonuclear leukocytes following ingestion.

Studies on the pathogenicity of group A streptococci. II. The antiphagocytic effects of the M protein and the capsular gel

A QUANTITATIVE STUDY OF THE COMBINED ANTIPHAGOCYTIC EFFECTS OF THE M PROTEIN AND THE HYALURONIC ACID CAPSULES OF FOUR STRAINS OF GROUP A STREPTOCOCCI REVEALED THE FOLLOWING FACTS RELATING TO THEIR INTRAPERITONEAL VIRULENCE IN MICE AND RATS: 1. The most virulent strain, S23M (matt), produced both a large hyaluronic acid capsule and a full complement of M protein, the combined effects of which rendered the organism highly resistant to surface phagocytosis. 2. The slightly less virulent strain, T14/46 (matt virulent) was somewhat more susceptible to surface phagocytosis owing to the fact that its smaller capsule was less antiphagocytic than that of the S23M organism. 3. The glossy variant of the S23 strain (S23G), which ranked third in virulence, was still more susceptible to surface phagocytosis because of its lack of detectable M substance. Its large hyaluronic acid capsule, however, was capable of protecting it against phagocytosis on glass. 4. The least virulent strain, T14 (matt avirulent), was the most susceptible of all to phagocytosis. Though it possessed both M substance and capsule, which together prevented its phagocytosis on glass, each of them was shown to be quantitatively and functionally deficient as compared to Strain S23M. The differences in phagocytability, which appear to be directly related to the pathogenicity of the organisms, could be adequately demonstrated in vitro only by phagocytic tests designed to measure surface phagocytosis in the absence of opsonins. This fact is in keeping with the observation, previously reported, that surface phagocytosis plays a critical role in the defense of the host, particularly during the earliest stages of experimental streptococcal infections. Its possible relation to suppuration during the later stages of infection is also discussed.

Studies on the pathogenicity of group A Streptococci. I. Its relation to surface phagocytosis

Four strains of Group A streptococci, possessing different degrees of virulence for both mice and rats, were tested for susceptibility to phagocytosis on glass slides, in glass roller tubes, and on the surfaces of freshly excised tissues and moistened filter paper. All of the tests were performed in the absence of serum to exclude the possible presence of opsonins. Only under conditions which allowed surface phagocytosis to take place was there a correlation between virulence and susceptibility to phagocytosis. A similar relationship between virulence and surface phagocytosis was also demonstrable in vivo during the early stages of experimental streptococcal peritonitis. Systematic study of the evolution of the peritonitis revealed that its outcome was determined by the phagocytic reaction which occurred in the first few hours of the infection.

Length of antibiotic therapy in in-patients with primary pneumonias

Seventy-three subjects with primary pneumonia in a hospital in Northern Nigeria were given antibiotics until they had been afebrile for 24 hours. The average duration of therapy was 2.54 days (about 60 hours), which is considerably shorter than the current recommended practice. Subjects with hepatosplenomegalic schistosomiasis and tropical splenomegaly syndrome required antibiotics for a significantly longer period (3.75 days) than those without either of these conditions. Those with an antigenaemia did not require antibiotics for a significantly longer period than those without an antigenaemia. There were no deaths, no increase in morbidity and in virtually all cases complete resolution of the lung lesion occurred within the expected time. It is suggested that in primary pneumonia it is more rational to stop antibiotics after the patient has been afebrile for 24 hours. This leads to a shorter stay in hospital and to the use of less antibiotic.

Surface phagocytosis; further evidence of its destructive action upon fully encapsulated pneumococci in the absence of type-specific antibody

Experiments recently reported (18) have been interpreted to indicate that surface phagocytosis plays no significant part in natural antipneumococcal defense. A repetition of these experiments has revealed: (a) that the cellular content of the leucocytic suspensions used in the phagocytic tests was of a different order of magnitude from that of the exudates which usually exist in infected tissues, (b) that the suspensions were too dilute to allow surface phagocytosis of pneumococci to occur, and (c) that the ratio of bacteria to leucocytes. was such that, when a sufficiently concentrated exudate was employed, the pneumococci injured the leucocytes and thus prevented phagocytosis from taking place. When conditions of the tests were suitably controlled, and conventional quantitative methods were employed to measure the end results of the phagocytic reaction, the essential observations relating to surface phagocytosis were fully confirmed. The significance of this non-antibody mechanism of defense in pneumococcal infections was thus further substantiated.

Fate of non-virulent group A streptococci phagocytized by human and mouse neutrophils

The fate of non-virulent group A streptococci phagocytized in vitro has been investigated by destroying the phagocyte with electric current and observing whether the liberated cocci multiply. Human and mouse peripheral blood neutrophils quickly injure ingested cocci, the time required to produce 50 per cent non-survival of chains being 8 and 6(3/4) minutes, respectively.

Phagocytosis of bacteria in the absence of antibody and the effect of physical surface; a reinvestigation of surface phagocytosis

The present experiments have shown that phagocytosis occurs in the absence of specific antibody and in the absence of a "suitable physical surface", as further that the presence of a rough surface does not increase the in vitro phagocytosis of pneumococci by polymorphonuclear leukocytes. This held true during repetition of Wood's experiments, as well as when more controlled quantitative techniques were employed, when conditions were made optimal for phagocytosis by increasing bacterial concentrations, and when blood leukocytes were substituted for exudate leukocytes. Evidence has been presented previously that the stimulation of phagocytosis of E. coli, B. abortus, and Type IV Pneumococcus, after contact with filter paper or an active compound present in filter paper, is a chemical effect rather than a physical effect. This type of stimulation did not occur with the Type I A5 Pneumococcus. The leukocyte of the circulating blood was found to be definitely superior to the exudate leukocyte in phagocytic capacity, under all the experimental conditions tested.

An experimental analysis of the curative action of penicillin in acute bacterial infections. II. The role of phagocytic cells in the process of recovery

Type I pneumococci injected into the leg muscles of otherwise normal mice reached a maximum total population of approximately 10(6) organisms. In mice rendered severely leucopenic by previous irradiation the maximum bacterial counts recorded were of the order of 10(9). Since the lesions in the latter animals were relatively acellular, the thousandfold difference in the two experiments represented a rough measure of the antibacterial action of the leucocytic exudate. The suppressive effect of the leucocytic exudate was shown by histologie studies to involve phagocytosis. The ingestion of pneumococci was clearly demonstrable within the first 12 to 18 hours. Accordingly, it was attributed to surface phagocytosis. In support of this conclusion was the finding that type III pneumococci reached a significantly higher total population in the myositis lesions than did type I. The type III strain used had been previously shown to be resistant to surface phagocytosis during active growth, whereas the type I strain was known to be susceptible throughout its growth phase. Evidence was also presented that the dense leucocytic exudate probably caused in addition a significant degree of bacteriostasis. When penicillin therapy was begun 9 hours after inoculation, the pneumococci were cleared from the lesions with equal rapidity regardless of the presence or absence of leucocytic exudate. At this early stage the pneumococci were multiplying rapidly in the lesions of both the irradiated and unirradiated mice and therefore were promptly killed by the direct action of the penicillin. When the start of treatment was delayed, however, until 24 hours after inoculation, the bacteria in both sets of lesions had already reached their maximum counts and therefore were presumably resistant to the bactericidal effect of the antibiotic. Under such circumstances the destruction of the bacteria was found to be significantly less prompt in the acellular lesions than in those with a normal cellular exudate. It is concluded from these findings that, in established pneumococcal myositis in mice, the curative effect of penicillin is due, not to the bactericidal action of the antibiotic alone, but rather to the combined effect of the drug and the cellular defenses of the host. The same conclusion also appears to be applicable to analogous acute infections in man, particularly when they are sufficiently advanced to be definitively diagnosed.

The mechanisms by which macrophages phagocyte encapsulated bacteria in the absence of antibody

EVIDENCE HAS BEEN PRESENTED: (1) that macrophages from experimentally produced inflammatory exudates are capable of phagocyting fully encapsulated Type I pneumococci and group A Friedländer's bacilli in the absence of antibody, (2) that the principal mechanisms involved are those of surface phagocytosis, and (3) that the majority of pneumococci ingested by macrophages in antibody-free preparations are ultimately destroyed. The relationship of these phenomena to the mechanism of recovery in pneumococcal and Friedländer's bacillus infections has been briefly discussed.