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Phagocytosis and killing of Brucella by human polymorphonuclear leukocytes
Abstract:
Although cellular immunity involving activated macrophages is important in resistance to Brucella, serum factors and polymorphonuclear leukocytes (PMNLs) play some role in the initial response to infection. The interaction between human PMNLs and virulent and attenuated strains of Brucella abortus and Brucella melitensis was studied by in vitro techniques. Virulent and attenuated strains of both species were rapidly phagocytosed after opsonization with normal human serum (NHS); nonopsonized bacteria were not phagocytosed. In contrast, NHS devoid of detectable antibodies was bactericidal for strains of B. abortus but not of B. melitensis. In addition, intracellular killing of ingested bacteria was shown for virulent B. abortus but not for B. melitensis. Ultrastructural studies revealed morphological alterations in about one-half of phagocytosed B. abortus and B. melitensis after incubation for 10 min; thereafter, nearly 100% of B. abortus showed some degree of degeneration, whereas B. melitensis remained intact during 120 min of observation.
Insights
Human polymorphonuclear leukocytes (PMNLs) and normal human serum (NHS) are crucial for the initial Brucella infection response. While NHS aids phagocytosis, its bactericidal effect and PMNLs
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Cellular immunity, particularly activated macrophages, is key in combating Brucella infections.
- Serum factors and polymorphonuclear leukocytes (PMNLs) contribute to the early stages of Brucella infection.
- Understanding the interaction between host immune cells and Brucella species is vital for developing effective treatments.
Purpose of the Study:
- To investigate the in vitro interaction between human PMNLs and both virulent and attenuated strains of Brucella abortus and Brucella melitensis.
- To elucidate the roles of normal human serum (NHS) and PMNLs in the initial phagocytosis and killing of Brucella.
- To compare the susceptibility of B. abortus and B. melitensis to innate immune mechanisms.
Main Methods:
- In vitro incubation of human PMNLs with opsonized and non-opsonized Brucella strains (B. abortus and B. melitensis).
- Assessment of bacterial phagocytosis by PMNLs.
- Evaluation of serum bactericidal activity using NHS with and without antibodies.
- Intracellular killing assays.
- Ultrastructural analysis of bacteria within phagocytic cells.
Main Results:
- Both virulent and attenuated Brucella strains were rapidly phagocytosed by PMNLs when opsonized with NHS; non-opsonized bacteria were not ingested.
- NHS without antibodies demonstrated bactericidal activity against B. abortus but not B. melitensis.
- Intracellular killing was observed for B. abortus but not for B. melitensis within PMNLs.
- Ultrastructural studies showed significant degeneration of B. abortus within 120 minutes, while B. melitensis remained largely intact.
Conclusions:
- Human PMNLs and NHS play a significant role in the initial innate immune response to Brucella infection.
- B. abortus is more susceptible to the bactericidal and intracellular killing activities mediated by NHS and PMNLs compared to B. melitensis.
- These findings highlight differential susceptibility of Brucella species to innate immunity, impacting host resistance.