In most patients, antibiotic treatment of Lyme arthritis (LA) combined with host immunity results
in spirochetal elimination, tissue repair and resolution of arthritis, called antibiotic-responsive LA.
However, despite spirochetal killing, some patients develop an inflammatory, proliferative
synovitis lasting months to several years after antibiotic therapy, called post-infectious (antibiotic-
refractory) LA. The synovial lesion in these patients is similar with that in other forms of chronic
inflammatory arthritis, including rheumatoid arthritis. The central feature in setting the stage for
post-infectious LA seems to be a sustained, excessive pro-inflammatory response, with
exceptionally high levels of IFN-¿, which overwhelms regulatory control mechanisms. In these
patients, persistent inflammation leads to further vascular damage, fibrosis, and autoimmune
phenomena in synovia, as seen in other forms of chronic inflammatory arthritis. We have shown
that this response may be accompanied by Lyme disease (LD)-associated autoantibodies, a
response that becomes T cell dependent and potentially pathogenic. In these patients, IgG4
autoantibodies in synovial fluid, but not antibodies of other subclasses, correlate with specific
synovial pathology – obliterative microvascular lesions and fibrosis. Moreover, obliteration of
blood vessels suggests cytotoxic immune responses, and our recent transcriptomic studies of
post-infectious LA synovial tissue show a strong cytotoxic gene signature, similar with that in RA.
In this grant, we will use a “systems serology” approach to understand functions of Borrelia
burgdorferi (Bb) antibodies and LD autoantibodies by delineating Fc receptor binding, binding
affinity, Fc glycans, antibody-dependent phagocytosis and antibody-dependent cytotoxicity in
antibiotic-responsive vs. post-infectious LA patients. In addition, we will define the types and
frequencies of lymphocytes with cytotoxic and inflammatory potential in peripheral blood and
synovial fluid in these two patient groups using flow cytometry, and will further delineate the
complete phenotype of implicated cytotoxic cells by single-cell RNA-sequencing. We will correlate
these data with determinations of cytokine, granzyme, and perforin levels in vivo in serum and
synovial fluid of these patients, as measured by Luminex. Finally, we will examine the cytotoxic
potential of implicated T cells in directly killing target cells, and indirectly by asessing the effects
of extracellular cytotoxic effector molecules on cells. This research has significant implications for
understanding pathogenesis and aiding in diagnosis and treatment of LA, and more generally, as
a human model of infection-induced chronic inflammatory arthritis.