Department of Pathology

Overall Mission of the Lab

To study the mechanisms used by pathogens to manipulate the innate immune system

Projects

Trehalose dimycolate Project

The cording phenotype exhibited by virulent mycobacteria is caused by TDM.

Trehalose 6,6’-dimycolate (TDM) is a primary immunostimulatory component of the cell wall of Mycobacterium tuberculosis (TB) and Complete Freund’s Adjuvant. It has been shown to individually reproduce many of the pathologic lesions associated with tuberculosis, to both stimulate or inhibit macrophage activity, to cause both necrosis and apoptosis, and has recently been shown to prevent phagosomal-lysosomal fusion in macrophages. This last effect is key to the persistence of TB in macrophages and the success of this pathogen. What is intriguing about this glycolipid, is that these effects vary depending on how the molecule is presented. For example, if TDM is coated onto a “bacteria-sized” latex particle, it does not stimulate macrophages; whereas if TDM is presented on a larger particle (i.e., greater than 10 mm in diameter) or as a monolayer or an emulsion, it stimulates Toll-like receptor signaling, MAPK pathway activation, and cytokine production. This project aims to identify how TDM inhibits macrophage activity in some forms while stimulating activity in other forms, through a combination of cell biological, molecular biological, immunological, and biochemical techniques.

Scavenger Receptor Project

Resident peritoneal macrophages.

In collaboration with the Bowdish laboratory at McMasters University, we are studying the role of class A scavenger receptors, MARCO and SRA, in tuberculosis infection. These receptors are expressed on the surface of macrophages and are involved in the non-specific binding and uptake of a variety of endogenous and exogenous proteins and lipids, most notably, LDL. We have recently shown that macrophage pro-inflammatory cytokine responses to TDM are mediated via a collaborative effort between MARCO, TLR2, and CD14. SRA can also mediate some macrophage responses to TDM, but this interaction is less specific and requires TLR4 and MD2, in addition to TLR2 and CD14. MARCO- and MARCO/SRA doubly-deficient macrophages also show markedly reduced pro-inflammatory cytokine responses to infection with TB. Interestingly, while cytokine responses are reduced, suggesting that infected macrophages are less activated, intracellular bacterial growth is inhibited. Based upon these findings, we hypothesize that infection of MARCO- and MARCO/SRA doubly-deficient mice with TB will result in altered histopathologic lesions and bacterial growth. We also hypothesize that exposure of MARCO-expressing macrophages to lipid particles may reduce uptake of TB while also reducing cytokine responses and intracellular growth. To test this latter hypothesis, we are collaborating with Dr. Anh Le at Emory University, who has provided us with fully characterized lipid particles purified from human patients. This project aims to understand the role of scavenger receptors in TB pathogenesis through the use of murine models, histopathology, and cell biological, biochemical, molecular biological, and immunological techniques.

Cytauxzoonosis Project

Pulmonary venules are completely occluded by adherent,
C. felis-infected monocytes.

Cytauxzoon felis is a highly fatal tick-borne disease of wild and domestic felids in most of the Southern United States. During the acute stage of this disease, this protozoal parasite infects intravascular monocytes, which markedly increase in size, and adhere to and occlude smaller blood vessels. Neutrophils, while uninfected, are also increased in number and have recently been shown to mediate many of the clinical signs associated with this disease. We hypothesize that the leukocyte adhesion molecule, CD18, is upregulated and highly expressed on the surface of infected macrophages and recruited neutrophils. This project aims to show that by administering neutralizing antibodies against CD18 to acutely infected cats, we can ameliorate the clinical signs and improve survival. This project will utilize a number of molecular and immunologic techniques, including immunohistochemistry, real-time RT-PCR, laser capture microdissection, flow cytometry, ELISA, and antibody production, as well as a clinical trial in infected cats. We will also attempt to optimize conditions for the culture of C. felis in order to further study cytauxzoonosis pathogenesis.

Last Reviewed July 29, 2010

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Dr. Sakamoto's Lab

Department of Pathology
College of Veterinary Medicine
The University of Georgia
Athens, GA 30602-7388

Front, left to right:
Kaori Sakamoto, Lindsey Megow, Karelma Frontera-Acevedo, Llewelyn Sellers, Mac Makemson.
Back, left to right:
Dhruv Chaudhary, Sang Dao

Institute Pasteur de Guadeloupe

Alveolar macrophage attacking E. coli. Photo by Dennis Kunkel.

Related Links

Kaori Sakamoto, DVM, PhD