Dept. of Microbiology & Immunology

University of Tennessee, Memphis

Mark A. Miller, Ph.D.

Office: (901) 448-6752

Lab: (901) 448-4679

mamiller@utmem.edu

Office: 701 M.S.B.

Lab: 716, 720 M.S.B.

Laboratory web page

Research Program

IL-12 adjuvanticity and the mucosal immune system. Pathogens can gain access to the human host either parenterally or via mucosal surfaces (e.g. inhalation, ingestion, sexual contact, etc.). The portals of entry for many potential pathogens of humans are the mucosal surfaces that line the respiratory, gastrointestinal, and urogenital tracts. There are a variety of innate and active immune mechanisms which protect these mucosal surfaces against invasion by potentially pathogenic organisms. Innate characteristics which serve this function include gastric acidity, peristaltic activity, intestinal mucus, pancreatic juice and bile, and resident microflora that compete for attachment sites along the epithelial linings. Mucosal surfaces are also protected by a very large (and apparently interconnected) local immune system, which essentially operates in anatomical and functional separation from the systemic immune system. For instance, parenteral immunization (subcutaneous, intravenous, intramuscular, etc.) evokes strong systemic responses but generally elicits poor responses at mucosal surfaces, while mucosal immunization (oral, intranasal) elicits heightened mucosal immune responses. The stimulation of mucosal immunity is believed to occur at specialized aggregates of lymphoid tissue referred to collectively as the broncus and gut associated lymphoid tissue (BALT and GALT). An interesting feature of the BALT and GALT regions is their ability to "communicate" immunological information arising at one mucosal surface to all other mucosal surfaces of the body, thus, stimulation of IgA precursor B cells in the Peyer's patches can be disseminated to the lamina propria of the intestinal, respiratory, and genitourinary tracts. This feature of the mucosal immune system suggests that oral or intranasal vaccine regimens, which are desirable due to ease of administration, could be effective for generating immunity in all areas of the mucosal immune system. Unfortunately, most immunogens elicit very weak and short-term mucosal immune responses, suggesting that novel immunization strategies will be required to allow mucosal immunization with well-defined protective antigens.

    In recent years, the use of cytokines as immunomodulators or adjuvants has gained popularity and has proven to have great potential. Of the cytokines being studied as adjuvant components, IL-12 appears to have the most promise. IL-12 is a proinflammatory cytokine produced by monocyte/macrophages, B cells, dendritic cells, and neutrophils in response to bacteria, intracellular pathogens, fungi, viruses, or their products. This cytokine has a broad range of immunomodulatory effects that, in general, act to promote cell-mediated immunity. Most notably, IL-12 has been shown to be a powerful signal driving the differentiation of naive CD4+ cells toward the Th1 phenotype, presumably through the stimulation of IFN- production. Moreover, numerous studies have demonstrated that exogenous IL-12 has tremendous potential as an adjuvant or therapeutic agent in the prevention or treatment of a variety of infectious diseases, allergic or autoimmune maladies, and even cancer.

    Over the last several years, I have worked to document the ability of IL-12 to promote responsiveness to otherwise non-immunogenic antigens. These studies have been performed using the murine Listeria monocytogenes infection model and have been designed to take advantage of the inability of heat-killed Listeria monocytogenes (HKLM) or subunit preparations of Listeria to elicit immune responses when injected alone. To investigate the potential adjuvanticity of IL-12, small amounts of this cytokine were co-administered with HKLM, and the resulting cell-mediated immune responses were measured using a variety of techniques. These studies clearly revealed that IL-12 potentiated potent, long-lived T cell-mediated immunity to Listeria. Further investigation revealed that IL-12 potentiated protective immunity when co-injected with a listerial antigen preparation designated soluble listerial protein (SLP), or with a synthetic peptide corresponding to an immunodominant segment of listeriolysin-O (LLO, a virulence factor produced by Listeria). These results demonstrated that IL-12 acts as an adjuvant for particulate, soluble, or peptide immunogens. Studies performed in genetic "knock-out" mouse strains and designed to investigate the mechanism of IL-12 adjuvanticity have also proved very interesting and have laid the groundwork for understanding the mechanism of IL-12 adjuvanticity.

    Although the effects of IL-12 on the development of systemic immune responses has been intensively studied in recent years, relatively little is known about its effects on the development of mucosal immune responses. It seems likely that incorporation of IL-12 into mucosal vaccine formulations could dramatically alter the Th phenotype of both mucosal and systemic responses raised against the immunogen of interest. We have initiated studies designed to characterize the mucosal and systemic responses (cellular and humoral) generated by immunization with the combination of immunogen and IL-12 while employing various methods designed to promote mucosal immunity. We also continue to investigate the mechanism(s) involved in the adjuvanticity of this remarkable cytokine.

Selected Publications

Mark A. Miller, Marianne J. Skeen, and H. Kirk Ziegler. 1995. Non-viable bacterial antigens administered with IL-12 generate antigen-specific T cell responses and protective immunity against Listeria monocytogenes. J. Immunol. 155:4817-4828.

Mark A. Miller, Marianne J. Skeen, and H. Kirk Ziegler. 1996. Protective Immunity to Listeria monocytogenes Elicited by Immunization With Heat-Killed Listeria and IL-12: Potential Mechanism of IL-12 Adjuvanticity. Annals NY Acad. Sci. 797:207-227.

Mark A. Miller. 1997. Antibody response to immunization (review). Curr. Opin. Inf. Dis. 10:183-189.

Mark A. Miller, Marianne J. Skeen, and H. Kirk Ziegler. 1997. A Synthetic Peptide Administered with IL-12 Elicits Immunity to Listeria monocytogenes. J. Immunol. (Cutting Edge) 159:3675-3679.

Mark A. Miller, Marianne J. Skeen, and H. Kirk Ziegler. 1998. Long-Lived Protective Immunity to Listeria monocytogenes is Conferred by Immunization with Particulate or Soluble Listerial Antigen Preparations Coadministered with IL-12. Cell. Immunol. 184:92-104.

Mark A. Miller, Marianne J. Skeen and H. Kirk Ziegler. 1999. Protective Immunity Conferred by Immunization with Heat-Killed Listeria monocytogenes is dependent on MHC class II and IFN- Expression and Independent of MHC Class I or Endogenous IL-12 Expression. J. Immunol. (submitted).