The role of macrophages in primary and secondary infection of mice with Salmonella typhimurium

The effect of immunosuppression on resistance to Rhodococcus equi in mice

Rhodococcus equi, a natural pathogen of horses, produces lesions in mice following experimental infection. The effect of various immunosuppressing agents on the sequential development of these lesions has been assessed by measuring the growth of R. equi following intravenous or intranasal challenge and by histological examination. Cyclophosphamide treatment of mice, challenged intranasally, resulted in the development of lesions not unlike that seen in experimental and natural infection in foals. Cortisone acetate also impaired bacterial clearance from the lungs and affected the accumulation of mononuclear cells at infective foci. Most of the agents chosen to impair macrophage function failed to affect the resistance of mice to R. equi. Carbon, carrageenan and silica failed to alter significantly the growth kinetics of R. equi. Dextran sulphate depressed the rate of pulmonary clearance of organisms and affected the ability of animals to eliminate R. equi following rechallenge. Overall, these results support other evidence that cell mediated immunity is involved in host resistance to R. equi and that activated macrophages play a role in acquired immunity to this organism.

[Effect of Propionibacterium granulosum KP-45 on the resistance to Listeria monocytogenes and Salmonella typhimurium infections]

Killed bacterial cells of Propionibacterium granulosum KP-45 were found to be potent modifiers of non-specific resistance of mice against infection with either Listeria monocytogenes or Salmonella typhimurium. Injection of P. granulosum 7 days prior to infection resulted in marked splenomegaly. Disseminated acute inflammatory foci were found histologically in the liver. These mice were apparently less susceptible to infection, since definitely lower bacterial counts were determined. Simultaneous application of both P. granulosum KP-45 and L. monocytogenes resulted, however, in increased susceptibility of mice to infection, since definitely higher bacterial counts were found and the inflammatory reaction to infection was markedly enhanced.

Outer-membrane permeability of bacteria

Gram-negative bacteria evolved to survive under the conditions in which a number of hazardous compounds are abundant. The outer membrane which protects the cell interior acts as a barrier against such hazardous agents, yet the cells must incorporate the chemicals that are essential for the cellular activity. The devices that Gram-negative bacteria developed to incorporate such essence are the transmembrane pores. These pores could be subdivided into three categories: (1) pore made of porins has a weak solute selectivity; (2) pore made of lamB protein and tsx proteins hold intermediate solute specificity. and (3) pores for the diffusion of vitamin B12 and ferric ion-chelator complexes have a tight solute specificity. Porins are identified from a number of Gram-negatives and from the outer membrane of mitochondria of various sources. Studies on the diffusion properties of these outer-membrane proteins provided essential information to understand membrane transports.

Effect of in vivo administration of different adjuvants on the in vitro candidacidal activity of mouse peritoneal cells

The candidacidal activity (CA) of peritoneal cells (PC) in vitro was used as a measure of nonspecific microbicidal activity of phagocytes after intraperitoneal injection of mice with different adjuvants. Dilutions of PC were incubated with constant numbers of C. parapsilosis in a 96-well culture plate. The PC number causing 50% reduction of yeast colonies formed after 48 hr at 37 degrees C was called 1 CA50 unit. CA was expressed in CA50 units per 10(6) PC. Optimal reduction of the number of viable candida cells in vitro was established within 1.5 hr while 50% reduction was reached after 0.5 hr. In this test CA was, within limits, independent of the number of viable candida cells added per well (22 to 152 yeast cells), of the concentration of fetal calf serum (1-20%) and of the presence of heat-labile serum components. The CA of PC of individual mice was measured 6, 24, and 96 hr after injection of an adjuvant. In most instances optimal CA was observed 6 hr after administration of adjuvant and varied from 3.7 (methylamine) to 50 (Corynebacterium parvum strain 4982) units. With respect to the titer and duration of CA, the adjuvants were arranged in the following order of increasing efficacy: methylamine, heparin, polyol L 121, suramin, dextran sulfate, polyol L 101, dimethyldioctadecylammonium bromide, Liquoid, heat-killed Listeria monocytogenes, formalin-killed C. parvum strain 10387, and strain 4982. The CA induced by the latter strain persisted at least till 96 hr after injection. The induction of CA was accompanied by recruitment of polymorphonuclear cells. The contribution of distinct phagocytic effector cells to CA and the correlation between modulation of the specific and nonspecific immunity are discussed.

Virulence of different strains of Listeria monocytogenes serovar 1/2a

Different strains of Listeria monocytogenes serovar 1/2a were used to infect mice. A smooth, haemolytic strain multiplied in the spleen of normal adult mice and induced a long-lasting immunity to subsequent challenge infection. When the animals were treated with dextran sulphate (DS) Listeriae multiplied more rapidly and death followed within a few days. When normal baby mice were infected with this organism, fatal infection occurred. In nude mice a chronic infection developed. Secondly, a rough, haemolytic strain was used to infect mice. In normal adult mice no multiplication of this strain was observed. This holds true also for DS-treated animals. In nude mice the bacteria were eliminated slowly. Normal baby mice could only be killed if the infective dose was increased. This strain was considered to be intermediate in virulence. The infection stimulated a considerable immune response in mice, although to a lesser degree than the smooth, haemolytic Listeria strain. Thirdly, a smooth, non-haemolytic strain of L. monocytogenes serovar 1/2a was used. The bacteria were rapidly eliminated in normal, in DS-treated and in nude animals. Normal baby mice did not develop fatal disease, so it was considered that this strain of L. monocytogenes serovar 1/2a was avirulent. This variant was found to be non-immunogenic. A boosting of immunity of animals by this avirulent Listeria strain was, however, found to be possible. A reasonable explanation for the rapid elimination of avirulent L. monocytogenes serovar 1/2a from mice cannot be presented at this time. Whereas it is known that the macrophage system and the T-lymphocytes play an essential role in the resistance to virulent Listeriae, there is no increased susceptibility of the avirulent bacteria to these defence mechanisms. Other bacterial properties, such as serum sensitivity and lysozyme susceptibility, are likewise considered to be unimportant.