Serum-mediated immune cellular responses to Brucella melitensis. I. Role of a macrophage-stimulating factor in promoting ingestion of Brucella by streptomycin-protected cells

Sensitization and recall of anti-Brucella immunity in Guinea pig macrophages by attenuated and virulent Brucella

Peritoneal macrophages from guinea pigs vaccinated with strain Rev I of Brucella melitensis were only moderately activated thereby to limit, in an in vitro system, the intracellular growth of Rev I bacilli. Nevertheless, the appropriate memory cells had been primed, as demonstrated by the observation that reinfection of animals with virulent B. melitensis followed by intraperitoneal inoculation of mineral oil called forth macrophages in immunized guinea pigs which inhibited strongly the intracellular growth of brucellae. These macrophages slowed the growth of brucellae in the absence of immune serum. The intensity of the recall response was related to the challenge route and to the virulence of the challenge strain. After equal doses of attenuated or virulent brucellae, resistance was highest in macrophages recalled by the virulent strain. An important basis for the attenuation of the Rev I strain may lie in its initially low degree of macrophage activation during primary infection, although still retaining the capacity to prime stem cells. This property is associated with a protein found in fraction I, because 600 mug/ml in Freund's adjuvant primed guinea pigs so that challenge by strain 6015 evoked activated macrophages. This was seen microscopically as a reduced spread of infection in and amongst the macrophage population. Immune serum further reduced this spread and limited the number of viable intracellular brucellae.

Intracellular concentrations of antibacterial agents and related clinical implications

Intracellular penetration, accumulation and disposition of antibacterial agents is crucial for effective treatment of infections caused by intracellular bacteria. Intracellular concentrations and locations of both antibacterials and bacteria remain poorly understood and further research is needed to establish the importance of these concepts. For example, concepts that have been shown to be important outcome predictors when applied to concentrations of antibacterial agents in the serum include: (i) the effect of the peak antibacterial serum concentration to minimum concentration inhibitory to 90% of organisms (MIC90) for bacteria; (ii) the effect of length of time the serum antibacterial concentration remains above the MIC90 curve; or (iii) the area under the MIC90 curve, but above the serum antibacterial concentration curve. Further research should determine whether or not these concepts have important applications in an intracellular environment. Intracellular pathogens have been increasingly contributing to respiratory infections in the community. Therefore, on the basis of intracellular activity against bacteria causing respiratory infections, macrolides are favoured as the most broad spectrum class of oral antibacterial agents available for the treatment of patients with community-acquired respiratory infections.

Ability of mononuclear phagocytes from cattle naturally resistant or susceptible to brucellosis to control in vitro intracellular survival of Brucella abortus

The role of bovine mammary macrophages and peripheral blood monocyte-derived macrophages in natural resistance to bovine brucellosis was evaluated. A group of 11 naturally resistant and 10 chronically infected susceptible cows was studied following challenge with Brucella abortus. Macrophages from a greater proportion (P less than 0.026) of naturally resistant cows were significantly superior to macrophages from susceptible cows in their ability to inhibit the in vitro intracellular replication of B. abortus after challenge exposure. Studies of a second group of cows used mammary macrophages from 12 heifers and blood monocyte-derived macrophages from 22 bulls and heifers. These tests were completed before exposure to B. abortus, using mammary macrophages (P less than 0.039) and blood monocyte-derived macrophages (P less than 0.045), and also showed that macrophages from naturally resistant cattle were significantly superior in their ability to control the in vitro intracellular replication of B. abortus. Our data indicate that the mononuclear phagocytes from more than 80% of the resistant cattle controlled intracellular replication of B. abortus significantly better than did mononuclear phagocytes from susceptible cattle. Mononuclear phagocyte function appears to be an important factor in determining natural resistance to bovine brucellosis.

Vaccine and serum-mediated protection against brucella infection of mouse placenta

Pregnant mice inoculated i.p. or i.v. with virulent Brucella abortus Strain 544 displayed strong infection, evidenced by brucella enumeration in placentas and dams' spleens. Vaccination 1 month before pregnancy decreased frequency of placental colonization and number of brucella per infected placenta and per spleen. Protein-bound cell wall peptidoglycan (PG) fractions extracted from brucella protected mice as well as H38 killed and B19 attenuated living vaccines. The lipopolysaccharide (LPS) fraction was comparatively less active. Immune serum injected i.v., either 24 h before or just after i.v. challenge of 15-day pregnant mice effectively transferred resistance to placental colonization. Anti LPS, anti PG and anti killed brucella sera protected mice as well as vaccination one month before pregnancy. The immunity transferred persisted for at least 3 days.

Immune serum-mediated effects on brucellosis evolution in mice

Immune serum injected into mice before a footpad challenge of virulent strain Brucella abortus 544 can prevent dissemination of infection to the spleen. Sera from mice infected with Brucella for at least 2 months or from mice vaccinated with a protein-bound cell wall peptidoglycan Brucella fraction completely stopped dissemination. Brucella lipopolysaccharide and polysaccharide cross-reacting Yersinia immune sera reduced dissemination. Both peptidoglycan and lipopolysaccharide immune sera injected simultaneously with an intravenous challenge caused a shift in Brucella from spleen to liver. When immune sera were injected simultaneously with an intravenous challenge, the kinetics of splenic infection showed two effects: an early one, optimally measured at day 7 postchallenge, showed reduced numbers in the spleen due to the shift of Brucella to the liver; a late effect, measured at day 21 postchallenge, showed reduced numbers in spleen and liver with nearly complete clearance by day 49 postchallenge. Brucella lipopolysaccharide and cross-reacting bacterial antisera induced the early effect only, whereas peptidoglycan and infected mouse sera induced both effects. When peptidoglycan immune serum was injected 2 or 7 days after intravenous challenge, the late effect was somewhat reduced. Hence, immune sera to protein and polysaccharide surface antigens can (i) prevent dissemination of systemic infection and (ii) help destroy intercellular bacteria (protein antigen only). These effects may represent a large part of vaccinal immunity.

Macrophage membranes viewed through a scanning electron microscope

When rabbit peritoneal macrophages were cultured in serum and Tyrode medium, numerous membranous structures varying in size and transparency were observed to cover the surface in complex cascading patterns. Modifications in the methods of fixation and drying probably accounted for the new perspective of macrophage surfaces gained in this study.

Serum-mediated immune cellular responses to Brucella melitensis. IV. Infection of macrophages under anaerobic conditions

Immune mechanisms active against Brucella were studied under conditions of oxygen deficiency. B. melitensis grew in rabbit serum-Tyrode medium flooded with N(2) and CO(2) gas mixtures. Immune sera from rabbits injected with B. melitensis strain Rev I possessed growth-inhibitory activity that operated in anaerobic environments against Rev I and virulent strain 6015. When mixed with macrophages, immune sera mediated even greater inhibition of bacterial growth and slowed the spread of infection throughout the tissue culture. Although under anaerobic conditions the rate of phagocytosis was reduced, the macrophages in immune serum killed significant percentages of Brucella, suggesting that an antibacterial mechanism had been activated. Sonic extracts of macrophages prepared and tested under anaerobic conditions depressed the growth rate of strain Rev I. The extracts, however, exhibited no immediate killing capacity when tested in Tyrode solution. A factor from serum was required for depression of the growth rate.