EXPERIMENTAL PNEUMONIA IN MICE FOLLOWING THE INHALATION OF STREPTOCOCCUS H?MOLYTICUS AND OF FRIEDL?NDER'S BACILLUS

The results of these experiments support the previous observations that mice react in different ways to the inhalation of different bacteria. If normal mice are sprayed with hemolytic streptococci or Friedländer''s bacillus, these organisms may be recovered from the lungs and heart''s blood for a number of days after exposure. A large number of mice so exposed die of a septicemia during the 30 days following spraying. Consolidation of one or more lobes is not rare. If normal mice are exposed to an atmosphere of pneumococci, however, the organisms rapidly disappear from the lungs and only an occasional mouse succumbs to pneumococcus septicemia. In order to cause the pneumococcus to invade, the mice must first be alcoholized. If mice are first alcoholized and then exposed to a pneumococcus atmosphere, the pneumococci persist for a longer time in the lungs and a number will die of septicemia, a state of affairs which resembles that seen after the administration to normal mice of the other two organisms studied. In order to produce pneumococcus lobar consolidation, however, the mice must be first partially immunized and then allowed to inhale the organisms while under the influence of alcohol. A large percentage of both the normal and immune mice so alcoholized die within 5 days of exposure. There also appears to be a definite relation between the mortality and the length of time inspired bacteria persist in the lungs. Whether this lag in removal allows multiplication of the bacteria and massive infection to occur has not been determined. Following inhalation of pneumococcus, the organisms were either removed rapidly and without apparent detriment to the animal, or, as in the case of the alcoholized mice, invasion occurred, in which event the mouse usually succumbed rapidly, localization in the lung only occurring in partially immune animals. In the case of the hemolytic streptococci and Bacillus friedlænderi, however, the whole process of removal and infection seems to be slower. Infection and pneumonia occurred more often. These organisms seem to possess much greater invasive power when inhaled than the pneumococcus, though on intraperitoneal or subcutaneous inoculation, pneumococcus is highly virulent for normal mice.     

SUSCEPTIBILITY OF RABBITS TO INFECTION BY THE INHALATION OF VIRULENT PNEUMOCOCCI

1. Rabbits are very susceptible to infection by inhalation of Type I pneumococci. 2. When rabbits are exposed to a pneumococcus spray the bacteria readily penetrate into the lower respiratory tract. The pneumococci which reach the periphery of the lungs as a result of this procedure usually disappear within a few hours but a generalized and fatal septicemia frequently later appears. Pneumococci may then be recovered from the periphery of the kidney, liver, and spleen. In the animals which die pleurisy and pericarditis are common but pneumonia does not occur. 3. Rabbits may recover from pneumococcus septicemia.     

THE DEMONSTRATION OF LESIONS AND VIRUS IN THE LUNGS OF MICE RECEIVING LARGE INTRA-PERITONEAL INOCULATIONS OF EPIDEMIC INFLUENZA VIRUS

Following the intraperitoneal inoculation of mice with large doses of epidemic influenza virus (50,000 to 1 million intranasal M.L.D.) it can be recovered from the lungs in high concentration, and pulmonary lesions of moderate extent may be observed. The virus reaches its highest titer in the lungs 48 to 72 hours after intraperitoneal injection and may persist for 10 days. Virus may be recovered from the blood in the first 24 hours, but is readily detected in the omentum and peritoneum for 5 to 6 days. Mice which as a result of the intraperitoneal injection of virus show a high concentration of virus in the lungs do not die but become solidly immune to intranasal infection. Moreover, as early as 24 to 48 hours after intraperitoneal inoculation of large amounts of virus the animals may exhibit resistance to infection with fatal doses of virus given intranasally. Influenza virus given intravenously to mice is rapidly removed from the blood but persists in the lungs and induces pulmonary lesions. Virus can also be recovered from the liver for several days. With subcutaneous inoculation of influenza virus, however, the virus does not reach the blood or lungs in detectable amounts although the regional lymph nodes may yield considerable quantities of the agent. A brief consideration is presented of the mechanisms of infection and resistance which may be involved.     

Mice that exclusively express TLR4 on endothelial cells can efficiently clear a lethal systemic Gram-negative bacterial infection

Recognition of LPS by TLR4 on immune sentinel cells such as macrophages is thought to be key to the recruitment of neutrophils to sites of infection with Gram-negative bacteria. To explore whether endothelial TLR4 plays a role in this process, we engineered and imaged mice that expressed TLR4 exclusively on endothelium (known herein as Endothelium^TLR4 mice). Local administration of LPS into tissue induced comparable neutrophil recruitment in Endothelium^TLR4 and wild-type mice. Following systemic LPS or intraperitoneal E. coli administration, most neutrophils were sequestered in the lungs of wild-type mice and did not accumulate at primary sites of infection. In contrast, Endothelium^TLR4 mice showed reduced pulmonary capillary neutrophil sequestration over the first 24 hours; as a result, they mobilized neutrophils to primary sites of infection, cleared bacteria, and resisted a dose of E. coli that killed 50% of wild-type mice in the first 48 hours. In fact, the only defect we detected in Endothelium^TLR4 mice was a failure to accumulate neutrophils in the lungs following intratracheal administration of LPS; this response required TLR4 on bone marrow–derived immune cells. Therefore, endothelial TLR4 functions as the primary intravascular sentinel system for detection of bacteria, whereas bone marrow–derived immune cells are critical for pathogen detection at barrier sites. Nonendothelial TLR4 contributes to failure to accumulate neutrophils at primary infection sites in a disseminated systemic infection.     

EFFECT OF SPLENECTOMY ON THE SUSCEPTIBILITY OF MICE INOCULATED WITH DIPLOCOCCUS PNEUMONIAE

An experimental model is described which demonstrated increased susceptibility of mice to infection with D. pneumoniae following splenectomy. It was necessary to use small numbers of a particular strain of pneumococcus (D. pneumoniae type 6), intravenous infection and a particular strain of mouse (pathogen-free NCS strain). The increase in susceptibility persisted for at least 4 months after splenectomy. With modifications in experimental design such as use of large numbers of organisms, a different strain of pneumococcus, the intraperitoneal route of infection or a different mouse strain no increase or a much less impressive increase in susceptibility was demonstrated. Following intravenous injection of small numbers of D. pneumoniae Type 6 bacteremia tended to persist in all NCS mice. Multiplication of pneumococci subsequently occurred in a higher proportion of mice with splenectomy and at a more rapid rate than in control animals. Mice with splenectomy usually had more D. pneumoniae per ml of blood than per gram of any tissue. This suggested that in these mice multiplication of microorganisms occurs primarily in blood. In control mice higher concentrations of bacteria were present in spleen than in blood, and higher concentrations were found in blood than in other tissues. These results suggested that in normal mice infected intravenously with small numbers of D. pneumoniae Type 6, the spleen protects by removing and killing small but critical numbers of D. pneumoniae which are circulating in the blood. No evidence was found to suggest that the altered susceptibility is mediated by an effect of splenectomy on numbers of circulating leukocytes or on the antibacterial activity of mouse blood.     

EXPERIMENTAL STUDIES OF THE NASOPHARYNGEAL SECRETIONS FROM INFLUENZA PATIENTS : V. BACTERIUM PNEUMOSINTES AND CONCURRENT INFECTIONS.

During the course of animal experiments with the anaerobic filter-passing organisms cultivated from epidemic influenzal sources, certain pulmonary infections with ordinary bacteria have been observed. The experiments also have shown that the lungs of animals infected with Bacterium pneumosintes are less resistant than normal lungs to infection with ordinary bacteria. The demonstration of this fact invites a comparison of the course of these experimental bacterial infections with the sequence of postinfluenzal pneumonias attributable to similar organisms in man. These observations furnish additional proof of the identity of Bacterium pneumosintes and the active agent derived from the nasopharyngeal secretions of patients in the early hours of epidemic influenza.     

ETIOLOGY OF YELLOW FEVER : VII. DEMONSTRATION OF LEPTOSPIRA ICTEROIDES IN THE BLOOD,TISSUES, AND URINE OF YELLOW FEVER PATIENTS AND OF ANIMALS EXPERIMENTALLY INFECTED WITH THE ORGANISM.

Examinations of fresh blood from yellow fever patients by means of the dark-field microscope, made in more than twenty-seven cases, revealed in three cases the presence of Leptospira icteroides. In no instance was a large number of organisms found, a long search being required before one was encountered. The injection of the blood into guinea pigs from two of the three positive cases induced in the animals a fatal infection, while the blood from the third positive case failed to infect the guinea pigs fatally. Careful but by no means exhaustive dark-field searches for the leptospira with fresh specimens of blood from the remaining cases of yellow fever ended without positive findings, although four of the specimens, when injected into guinea pigs, caused a fatal leptospira infection. Stained blood film preparations from the corresponding cases were also examined, but the percentage showing the leptospira in the blood was no greater than that found by examination in the fresh state with the dark-field microscope. In fact, owing to the defective stains that were available at the time of the investigation a great many slides did not take the proper coloration with Giemsa''s or Wright''s stain and could not be relied upon. Regarding the presence of Leptospira icteroides in various organs both dark-field and stained films were examined. In only one instance so far a few organisms were detected in the emulsion of liver taken shortly after death from a case dying on the 4th day of yellow fever. This part of the work will be reported later upon completion. Examinations of the urine from different cases of yellow fever were made both by dark-field microscope and by inoculation into guinea pigs. The results were totally negative in thirteen cases, including many convalescents, but in one case one of the guinea pigs inoculated with 10 cc. of the urine came down on the 15th day with suggestive symptoms (suspicion of jaundice, and some hemorrhagic and parenchymatous lesions of the lungs and kidneys). This specimen showed no leptospira by dark-field examination. In experimental infection of guinea pigs with Leptospira icteroides the blood became infective in many instances 48 hours after inoculation, and was always infective after 72 hours. The liver and kidney become infective simultaneously with the blood. Detection of the organism by means of the dark-field microscope has seldom been accomplished before the 5th day. The organisms are most abundant on the 6th to the 7th day, but become fewer or completely disappear before death. In the meanwhile the number of organisms increases in the liver and kidney, from which they disappear as the jaundice and other symptoms become aggravated. When death occurs these organs seem to have lost most of the leptospira) and positive transfer by means of them is less certain. At the later stage of the disease the blood is often free from the organisms and ceases to be infective. Positive transmission with blood obtained from moribund animals is not impossible, however, even when no leptospira can be detected under the dark-field microscope.     

EFFECT OF NUTRITION ON THE RESISTANCE OF MICE TO ENDOTOXIN AND ON THE BACTERICIDAL POWER OF THEIR TISSUES

Mice on inadequate nutritional regimens were found to be more susceptible to various bacterial diseases than mice fed a complete diet containing 15 to 20 per cent casein. The tests of susceptibility included: (a) infections with virulent bacteria; (b) injection of large doses of avirulent coagulase-negative staphylococci; and (c) lethal effects of bacterial endotoxins. The infection-enhancing effect of nutritional deficiencies could be rendered even more striking by administering the infective inoculum simultaneously with a sublethal dose of endotoxin. Despite their great susceptibility to infection, malnourished animals retained much of their ability to eliminate bacteria from the blood, liver, spleen, kidneys, and lungs, at least during the early phases of the infectious processes. This was true even when the animals had received endotoxin simultaneously with the infective dose. The results suggest that under the conditions of the present study, the nutritional state influenced the outcome of infection not primarily by affecting the fate of the pathogens in vivo, but rather by modifying the ability of the host to resist their toxic effects.     

CORYNEBACTERIAL PSEUDOTUBERCULOSIS IN MICE : I. COMPARATIVE SUSCEPTIBILITY OF MOUSE STRAINS TO EXPERIMENTAL INFECTION WITH CORYNEBACTERIUM KUTSCHERI

The susceptibility of mice to experimental infection with Corynebacterium kutscheri was studied by comparing the host response to this organism of mice obtained from 31 different colonies, representing 15 different genetic types. A standardized infective dose, administered intravenously, made it possible to separate the animals into two sharply differentiated groups. All the animals of the following colonies died: Swiss Lynch, Swiss R/J, A/Jax, Princeton, RFVL, and CF₁ (SPF). All the animals of the following colonies survived: CFW, ICR, Balb/C, BSVS, BRVR, RIII, YBR/He, DBA/2 (from 3 different colonies), and C57B1/6 (from 12 different colonies). The two highly inbred strains, Swiss Lynch and C57Bl/6, were selected as prototypes of susceptible and resistant animals respectively, for more detailed studies. Following injection of an infective dose of 0.2 x 10^–4 ml of culture of C. kutscheri, all Swiss Lynch animals died within 3 to 11 days (the majority within 4 to 7 days); whereas all C57Bl/6 animals survived. The outcome of the infection in each strain was independent of age and sex of the animals. In Swiss Lynch animals, the corynebacteria multiplied rapidly in lungs, liver, kidneys, and to some extent in the spleen. In C57Bl/6 mice, there was no increase of the corynebacterial population in the lungs, liver, or spleen, but multiplication occurred in the kidneys during the early phase of the infectious process with resultant abscess formation. However, the renal infection soon subsided leaving no residual pathology. C. kutscheri could not be recovered from any organs of C57Bl/6 mice sacrificed 16 days after infection. Homogenates of organs from Swiss Lynch mice obtained while the infection was progressing contained only typical C. kutscheri. In contrast, the lungs and livers of similarly infected C57Bl/6 animals occasionally yielded large numbers of small translucent colonies distinctly different from those of typical corynebacteria. The use of mouse strains differing markedly in response to experimental infection with C. kutscheri is presented as a biologic model lending itself to further studies concerning factors which condition resistance to corynebacterial pseudotuberculosis, a disease of practical importance for investigators conducting experiments with murine species.     

Experimental pyelonephritis. I. Effect of ureteral ligation on the course of bacterial infection in the kidney of the rat

A study has been made of the effect of ureteral ligation on the susceptibility of the kidney to pyogenic infection. In most experiments a strain of E. coli was employed as the test organism, being injected intravenously in varying quantity either before or after ureteral ligation. A few experiments were also carried out with S. marcescens. Preliminary observations were made on the distribution and persistence of E. coli following its inoculation into the blood stream of normal rats. Rapid reduction in number of bacteria in the circulation occurred during the first 30 minutes, but bacteriemia persisted at a comparatively low level for at least 48 hours. Large proportions of the inoculated bacteria were arrested and apparently destroyed in the liver, spleen, and lungs. Comparatively small numbers were deposited in the kidneys; nevertheless, these continued to be demonstrable during the 1st week, without notable tendency to increase or decrease, then disappeared during the 2nd week. There was no acceleration in rate of disposal of the bacteria in the kidney when a second injection was made 1 week after the first. In rats with one ureter ligated the number of bacteria lodging in the kidneys after intravenous inoculation did not differ from that found in normal animals. It appears, therefore, that the increased susceptibility of the obstructed kidney to infection via the blood stream is not attributable to an increased trapping of circulating bacteria. 4 to 6 hours after the intravenous injection, however, an increased number of bacteria could be demonstrated in the obstructed kidney, apparently due to local multiplication, and by the end of 24 hours purulent infection was usually obvious. A comparatively large number of bacteria was required to cause infection, even in the kidney with obstruction. This appeared to be related to the small proportion of the intravenous inoculum which lodged in the kidney initially. Although bacteria could be demonstrated in the normal kidney for a week or more following intravenous injection it was not possible to induce active infection with equal regularity by ligating the ureter throughout this time. During the first 3 days the majority of obstructed kidneys developed infection, but after 5 or more days this occurred in only a small proportion of animals so treated. The reason for the difference, in relation to interval between intravenous injection and time of ligation, is not apparent. When the ureter was ligated but no intravenous injection of bacteria was given, staphylococcal infection developed in the obstructed kidney within 2 weeks in about one-third of the animals. Reasons are given for the belief that this was blood-borne infection, and not the result of contamination at the time of operation. Staphylococci were not recovered from the normal rat kidney. These "spontaneous" staphylococcal infections seldom developed when E. coli was injected intravenously at the time of ureteral ligation.     

Treatment of Respiratory Klebsiella pneumoniae Infection in Mice with Aerosols of Kanamycin

Aerosols of kanamycin resulted in greater survival of mice challenged with respiratory Klebsiella pneumoniae than the same dosage given intramuscularly. Determinations of viable bacteria in the blood and lungs revealed that aerosolized kanamycin was most effective when infection was confined to the lungs. After the organisms had spread to other areas, however, aerosol therapy was still more effective than intramuscular therapy, but only one-half the infected mice survived.     

A LATENT VIRUS IN NORMAL MICE CAPABLE OF PRODUCING PNEUMONIA IN ITS NATURAL HOST

1. A virus capable of producing fatal pneumonia in mice has been isolated repeatedly from the lungs of certain apparently healthy mice. Not all mice carry the virus. It was obtained only from mice supplied by three breeders although mice from eight different sources were studied. 2. The virus was avirulent as it occurred in normal mouse lungs and became virulent only after serial mouse lung passage. It was strictly pneumotropic for mice and produced pneumonia when given intranasally but showed no evidence of infection when given by other routes. The virus was non-infectious for ferrets and did not become pathogenic for this species after numerous serial passages. It was also non-pathogenic for rabbits, guinea pigs, rhesus monkeys, voles, deer mice, skunks, wood-chucks, opossums, and Syrian hamsters. 3. All strains of the virus which have been tested have been immunologically identical, as indicated both by cross immunity and cross neutralization tests in mice. 4. The virus was antigenic both in mice and in rabbits and was readily differentiated from viruses of human influenza and of swine influenza by means of either cross immunity or cross neutralization tests. 5. The virus was also neutralized by about 30 per cent of normal human sera tested. 6. The virus was extremely labile, and suspensions prepared in saline or broth became inactivated within a few hours at room temperature. The addition of normal horse serum to the virus suspensions, however, exerted a definite stabilizing effect. 7. Ultrafiltration results indicated that the virus particles have a diameter of about 100 to 150 millimicrons. 8. Evidence is presented which indicates that this virus is different from other viruses which various investigators have found in normal mouse lungs.     

EXPERIMENTAL TRANSMISSION OF INFLUENZA VIRUS INFECTION IN MICE : I. THE PERIOD OF TRANSMISSIBILITY

An experimental model has been developed for the reproducible transmission of influenza virus infection from experimentally infected mice to uninfected cage mates. Infector mice transmit influenza virus infection most readily during the period 24 to 48 hours after initiation of their infection. This restricted period of transmission is not due to declining titers of infective virus in the nose, trachea, or lungs of infector mice after 48 hours of infection, since peak titers in these tissues are maintained for another 48 hours. A mouse-adapted strain of A2 virus was found to be more readily transmitted than the mouse-adapted CAM strain of influenza A1 virus, although the CAM strain induced higher pulmonary virus titers and more extensive lung lesions.     

Effects of ethanol on pulmonary inflammation in postburn intratracheal infection

Infectious complications are a major cause of mortality in trauma patients. Burn patients with prior ethanol exposure have a worse prognosis than those who sustain injury but had not been drinking. We examined pulmonary infection and lung pathology in mice given ethanol (1.2 g/kg) 30 minutes before being subjected to 13 to 15% total body surface area scald burn followed by intratracheal inoculation with Pseudomonas aeruginosa (1-2 x 10(3) colony-forming units [CFUs]). Survival was monitored for up to 48 hours. Sham control groups had 100% survival after intratracheal infection regardless of ethanol exposure. Infected burned animals had 55% survival; however, survival of infected mice exposed to ethanol and burn injury was significantly lower (27%, P < .0001). When pulmonary infection was evaluated, the lungs of sham groups were negative for bacterial colonies. In addition, at 24 hours there were no significant differences in lung CFUs from infected burned animals regardless of ethanol exposure (3.0 x 10(4)). However, pulmonary bacterial content significantly decreased (1.2 x 10, P < .02) at 48 hours in mice given burn injury alone, where CFUs from the lungs of mice exposed to ethanol prior to burn did not decline (5.4 x 10(5)). At the same time point, lungs from animals given ethanol and burn injury had about a 2-fold (P < .02) increase in leukocyte infiltration and vascular congestion, as well as decreased pulmonary oxygen saturation (82.8%, P < .02), when compared with other treatment groups. In summary, ethanol exposure in postburn intratracheal infection results in the inability to clear pulmonary infection marked by a prolonged pulmonary leukocyte accumulation and a decrease in pulmonary function.     

Protease-activated receptor-1 impairs host defense in murine pneumococcal pneumonia: a controlled laboratory study

Introduction

Streptococcus pneumoniae is the most common causative pathogen in community-acquired pneumonia. Protease-activated receptor-1 (PAR-1) is expressed by multiple cell types present in the lungs and can be activated by various proteases generated during acute inflammation. The cellular effect of PAR-1 activation partially depends on the specific protease involved. We here determined the role of PAR-1 in the host response during murine pneumococcal pneumonia.

Methods

Wild-type (WT) and PAR-1 knockout (KO) mice were infected intranasally with viable S. pneumoniae and observed in a survival study or euthanized at 6, 24 or 48 hours of infection.

Results

PAR-1 KO mice had a better survival early after infection compared to WT mice. Moreover, PAR-1 KO mice had lower bacterial loads in lungs and blood at 24 hours and in spleen and liver at 48 hours after infection. This favorable response was accompanied by lower lung histopathology scores and less neutrophil influx in PAR-1 KO mice.

Conclusion

PAR-1 impairs host defense during murine pneumococcal pneumonia.     

Aerosol Phage Therapy Efficacy in Burkholderia cepacia Complex Respiratory Infections

Phage therapy has been suggested as a potential treatment for highly antibiotic-resistant bacteria, such as the species of the Burkholderia cepacia complex (BCC). To address this hypothesis, experimental B. cenocepacia respiratory infections were established in mice using a nebulizer and a nose-only inhalation device. Following infection, the mice were treated with one of five B. cenocepacia-specific phages delivered as either an aerosol or intraperitoneal injection. The bacterial and phage titers within the lungs were assayed 2 days after treatment, and mice that received the aerosolized phage therapy demonstrated significant decreases in bacterial loads. Differences in phage activity were observed in vivo. Mice that received phage treatment by intraperitoneal injection did not demonstrate significantly reduced bacterial loads, although phage particles were isolated from their lung tissue. Based on these data, aerosol phage therapy appears to be an effective method for treating highly antibiotic-resistant bacterial respiratory infections, including those caused by BCC bacteria.     

EXPERIMENTAL STUDIES OF THE NASOPHARYNGEAL SECRETIONS FROM INFLUENZA PATIENTS : III. STUDIES OF THE CONCURRENT INFECTIONS.

1. Concurrent infections in the experiments described may be regarded as of accidental nature and are not causally related to the typical effects induced in rabbits by a material wholly free from ordinary bacteria. 2. The influenzal agent exerts an effect on the pulmonary tissue which encourages the invasion of the lung and subsequent multiplication there of ordinary bacteria, such as the pneumococcus, streptococcus, and Bacillus pfeifferi. 3. A similarity is believed to exist between the conditions under which concurrent infections arose in the inoculated rabbits and those which seem to favor the occurrence of concurrent infections during epidemic influenza in man. In no instance did death occur in the rabbits as a result of the uncomplicated effects of the influenzal agent alone. When death occurred in any of the inoculated animals concurrent infection of the lungs by ordinary bacteria was present. The microorganisms most commonly met with under these conditions were Pneumococcus Type IV and atypical Type II, streptococci, and hemoglobinophilic bacilli. Other kinds were encountered less often.     

THE SOURCE OF THE MICROORGANISMS IN THE LUNGS OF NORMAL ANIMALS

It has been possible to show that the lungs of such animals as the calf, rabbit, guinea pig, white rat, and white mouse are readily invaded by organisms. The most frequent types observed in cultures from the border of the lungs have been streptothrix, molds, and bacteria of the Bacillus subtilis group. These forms originate in certain dry food stuffs (hay and straw). By withholding or moistening these materials it has been possible to diminish the number of organisms in the lungs. When these materials have been supplied to mice whose lungs under usual conditions contain only a few organisms, the number of positive cultures increases and is comparable with those of the larger animals. The bronchial lymph glands of all guinea pigs examined developed, in 66⅔ per cent of the tubes, organisms similar to those obtained from the lungs.     

REACTIONS OF RABBITS TO INTRACUTANEOUS INJECTIONS OF PNEUMOCOCCI AND THEIR PRODUCTS : VII. THE RELATION OF HYPERSENSITIVENESS TO LESIONS IN THE LUNGS OF RABBITS INFECTED WITH PNEUMOCOCCI

1. The intratracheal injection of egg albumin or pneumococcus protein induces an inflammatory reaction in the lungs of rabbits previously inoculated with the respective antigen. 2. A similar reaction occurs following intratracheal injection of pneumococcus protein into the lungs of rabbits previously inoculated with heat-killed suspensions of the bacteria. 3. This reaction appears to be related to the presence of circulating antibody and to have the nature of the Arthus reaction. 4. A study of the reaction of the lung of rabbits to infection caused by intravenous injections of Pneumococcus reveals that (a) reactions occur irregularly in the lung; (b) in the lungs in which reactions do occur, the histological changes are not different in normal rabbits and in rabbits made resistant by previous intravenous or intracutaneous injections of pneumococci. 5. Intratracheal injection of pneumococcus protein followed by intravenous injection of virulent pneumococci on the next day does not alter the course and character of the infection in resistant rabbits. 6. The experiments reported in this paper bring no evidences to support the view that the lesions in the lungs of rabbits following the intravenous injection of pneumococci are modified by any previous state of sensitivity.     

STUDIES ON THE HETEROLOGOUS IMMUNOGENICITY OF A METHANOL-INSOLUBLE FRACTION OF ATTENUATED TUBERCLE BACILLI (BCG) : I. ANTIMICROBIAL PROTECTION

Small quantities of the non-toxic residue of phenol-killed, acetone-washed, and methanol-extracted tubercle bacilli of the BCG strain conferred a high degree of resistance on mice against otherwise lethal experimental infection with Klebsiella pneumoniae and with a number of other pathogenic bacteria. The heightened resistance reached a peak within 24 hours after administration of the fraction, but was already discernible immediately thereafter. A period of reduced resistance was not observed. The state of heightened resistance was invariably manifested for at least 10 days, and could frequently still be demonstrated after several weeks or months. The methanol-insoluble fraction was immunogenically active even in experimental circumstances under which living BCG exerted no effect. Its protective effect was more marked in females than in males. The optimum dosage must be determined empirically vis-á-vis the strain of infecting organisms and the experimental parameters of administration and testing. Administration of the fraction to breeding females reduced the incidence of a naturally occurring endemic pneumonitis among their young, and increased considerably the breeding productivity of the mothers. These effects were manifested as late as 11 months after treatment.