Modulation of Natural Killer Cell Activity

Natural killer (NK) cells are a heterogenous subpopulation of peripheral blood lymphocytes (PBL) that have the ability to kill various tumors and tumor cell lines in the absence of prior sensitization. These cells have generated considerable interest and have been implicated in natural resistance to tumors,'-5 resistance to viral infection:-7 transplantation rejection,'** and immunoregulation of both T and B cells.e'' Recently, there has been evidence that NK cells or large granular lymphocytes (LGLs) are also involved in host resistance against bacterial infections. This has been demonstrated by the bactericidal activity of NK-like cells against certain bacteria such as Shigella and Salrn~nel la . '~'~ In addition to these interactions, there are several reports that demonstrate bacterial activation and/or recruitment of NK and NK-like cells presumably through the production or action of interferon, interleukin-2, and/or lipopolysaccharide (LPS).'z*'6'8 Under certain conditions this augmentation may be inhibited by LPS,I7 which attests to the complex nature of the microorganism-host interactions. Furthermore, the NK cell killing of infected host cellsI5 or local inflammation secondary to the killing of extracellular microorganisms may be responsible for the tissue destruction seen in various bacterial infections. The humoral and cellular responses in Lyme borreliosis have recently been under active investigation. While the humoral antibody response to Borrelia burgdorferi is well characterized, the cellular immune response is not well defined. However, it is known that a strong specific T cell response to B. burgdorferi occurs early in the course of the disease. This response may even precede the development of a measurable antibody response in some cases.I9 Once established, this response is long lasting. In this report, the cellular immune response to B. burgdorferi is further investigated. Specifically, the modulation of NK cells and N K cell activity by B. burgdorferi both in vivo and in vitro is characterized and discussed.