Persistence of Rickettsia prowazekii in cotton rat macrophage cultures.

Rickettsia prowazekii is able to multiply and persist for a long time in cotton rat macrophage culture (29-days observation period). Electron microscopic studies showed that the structure of Rickettsiae remained intact at different intervals post-inoculation (p.i.). In the course of persistence Rickettsiae revealed a reduced capacity to infect chick embryos and guinea pigs, however, the infectious agent could be isolated at all stages of persistence of cultured cells such as fibroblasts of the guinea pig embryo, macrophages of intact cotton rats.

Electron microscopic analysis of in vitro interaction of Rickettsia prowazekii with guinea pig macrophages. II. Macrophages from immune animals.

Alike to macrophages from intact animals, reproduction, destruction and formation of spheroplast-like forms were observed in macrophages from immune guinea pigs 2 months post-infection (p.i.) with the virulent Breinl strain of Rickettsia prowazekii. Unlike to the former, immune macrophages revealed phagolysosomes which were larger in size and contained more rickettsiae showing morphologic signs of destruction. Spheroplast-like forms occurred more often and were more numerous than in intact animals. Structures morphologically similar to L-forms of gram-negative bacteria and that of chlamydiae were also detected. After adding immune serum, more intact rickettsiae and spheroplasts were found in phagosomes as well as more phagolysosomes contained rickettsiae and spheroplasts with morphologic signs of destruction. It is suggested that clearance of immune macrophages from rickettsiae is mediated by at least two processes: on one hand by destruction of rod-shaped rickettsiae within phagolysosomes and, on the other hand, by formation and subsequent destruction of spheroplast-like forms within vacuoles, which probably also function as phagolysosomes.

Electron microscopic analysis of in vitro interaction of Rickettsia prowazekii with guinea pig macrophages. I. Macrophages from nonimmune animals.

Monolayer cultures of peritoneal macrophages of intact guinea pigs were infected with Rickettsia prowazekii (strain Breinl) and examined by electron microscopy after 30 min, 4 and 24 hr post-infection (p.i.). Three parallel processes developed in infected macrophages: reproduction of rickettsiae in macrophage cytoplasm, destruction in phagolysosomes and production of spheroplast-like forms. Reproduction of rickettsiae yielded 2 cell types: those with dense and with light cytoplasm; they were located side by side in the microcolony and seemed to have a common capsule-like coat. Relatively small spheroplast-like forms of about 1 micron in size were regularly detected. Addition of immune serum to macrophages increased the number of rickettsiae, both of rod-shaped as well as of spheroplast-like ones located within phagosomes, but elicited no increase in the number of digested pathogen cells.

[Antigen isolation from Rickettsia prowazekii cultured in FL cells and its use in the macrophage migration inhibition reaction]. / Poluchenie antigena iz rikketsii Provacheka, kul'tiviruemykh v FL-kletkakh, i ispol'zovanie ego v reaktsii ingibitsii migratsii makrofagov.

An antigen obtained from R. prowazekii cultivated in hydrocortisone-treated FL-cells possesses activity determined in the complement fixation test and the macrophage migration inhibition test. Such antigen can be used in the macrophage migration inhibition test with macrophages obtained from animals immunized with the preparations of rickettsial egg cultures.

Multiplication of Rickettsia prowazekii in cotton rat macrophage cultures.

The susceptibility of cotton rat macrophages to Rickettsia (R.) prowazekii, the percentage of the affected cells, and the intensity of damage to individual cells by rickettsiae were found to be much higher than those in guinea pig macrophages infected under similar conditions. At the same time, cotton rat macrophages proved to be more resistant to the effect of rickettsiae than guinea pig macrophages. Some common features of infection in cell culture and in animals have been observed. It is suggested that the outcome of interaction of rickettsiae with macrophages of one or another animal species may be important in generating acute or persistent infection.

[Macrophage migration inhibition test in guinea pigs infected with Rickettsia prowazekii]. / Reaktsiia ingibitsii migratsii makrofagov u morskikh svinok, zarazhennykh rikketsiiami Provatseka.

The process of infection caused by R. prowazekii (strain Breinl) in guinea-pigs was accompanied by the development of delayed type hypersensitivity manifested by the macrophage migration inhibition test (MMIT). This reaction could be detected on week 2 after the subcutaneous inoculation of the infective agent, achieved its maximum on weeks 3-4 with individual fluctuations taken into account and decreased by week 5 remaining at a low level during the whole period of the study (63 days). The period when the MMIT was most pronounced correlated with the period of the maximum increase in the titers of complement-fixing antibodies and the presence of the infective agent in the animal body.

Activity of macrophages from guinea pigs at various periods after infection with Rickettsia prowazeki.

The function of peritoneal macrophages from Rickettsia prowazeki-infected guinea pigs at various intervals of postinfection immunity was studied. The activity of macrophages in immunized animals was higher than in non-immunized ones; it was the highest in the period of the highest level of immunity and high levels of complement-fixing antibodies.

[In vitro study of function of macrophages obtained from intact and immune animals with experimental rickettsial infections]. / Izuchenie in vitro funktsii makrofagov, poluchennykh ot intaktnykh i immunnykh zhi votnykh pri éksperimental'noi rikketsioznoi infektsii.

The studies carried out on Rickettsia prowazekii (strain Breinl) have shown that these organisms can proliferate in the culture of guinea pig peritoneal macrophages, and the character of their development in macrophages depends mainly on the infective dose. Macrophages obtained from immune animals seem to have undergone functional transformation, thus becoming capable of destroying the infective agent. The process of the destruction of Rickettsia was more active in the presence of guinea pig immune serum.