Date on Master's Thesis/Doctoral Dissertation

12-2025

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Microbiology and Immunology

Degree Program

Microbiology and Immunology, PhD

Committee Chair

Mitchell, Thomas C.

Committee Member

Casella, Carolyn

Committee Member

Bodduluri, Haribabu

Committee Member

Alard, Pascale

Committee Member

Lawrenz, Matthew

Committee Member

Matoba, Nobuyuki

Author's Keywords

Vaccine; antibody; pneumonic plague; immunity

Abstract

Pneumonic plague is caused by inhalation of the bacterial pathogen Yersinia pestis. The immune response during Pneumonic plague occurs in two phases; an initial asymptomatic phase followed by a highly inflammatory and destructive phase resulting in 100% mortality if left untreated. The rapid onset of severe disease following the asymptomatic phase makes it difficult to administer antibiotics in time to prevent lethal outcomes. Therefore, the development of an effective vaccine is likely needed to combat pneumonic plague in areas of the world where Y. pestis remains endemic. One candidate subunit vaccine is protective in mice, a natural host for Y. pestis, but failed to consistently protect non-human primates in pre-clinical efficacy trials indicating that improvements in the vaccine are needed. Development of a more efficient vaccine requires a thorough understanding of beneficial features of the immune response to guide changes in vaccine design. We adopted a strategy in which mice were intentionally given limiting vaccine doses to conduct correlation testing of several immune parameters in survivors versus non-survivors following bacterial challenge. The measured parameters included serum titers of all isotypes and subclasses of antibody and the average affinity of polyclonal antisera using a novel microsphere-based method, as well as kinetics of immune cell infiltration into lung by myeloid and lymphoid cells during early phases of pulmonary infection. Live animal imaging of bacterial spread in lung allowed us to compare bacterial burden with the immune parameters to identify those that were most consistently associated with protective immunity. We found that antibody titers were not predictive of survival regardless of isotype, IgG subclass, or average affinity. Neutrophil influx was highly correlated with bacterial spread, but in a manner that suggested they are merely markers of infection rather than mediators of a protective response. Effectively immunized mice were found, instead, to have increased numbers of alveolar macrophages in direct proportion to the extent to which the Y. pestis infection was controlled at all time points tested. T cells were recruited by 48 hours, when they were transiently correlated with protective immunity. Notably, B cell abundance was also correlated with immunity which was unexpected given the canonical view that B cells act at a distance before eventually seeding infected tissue as tissue resident memory cells. Further evaluation revealed that class-switched plasmablasts and memory B cell numbers were specifically elevated in animals that had controlled the infection. These findings indicate that the establishment of B cell memory may be an overlooked correlate of vaccine efficacy that should be evaluated as a guide for future efforts to improve the pneumonic plague vaccine.

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