James McLachlan
Associate Professor
Biography
My lab is interested in the role that antigen-specific CD4+ helper T cells play during a chronic bacterial infection where the bacteria persists in various organs for the life of the animal. My main interest is to understand how this “stalemate immunity” forms and why the immune system is incapable of clearing the infection but is somehow capable of keeping the bacteria from overwhelming and killing the animal. To address this, we are using a mouse model of chronic Salmonella infection, the causative agent of typhoid fever. This infection becomes chronic in the mouse and immunity relies on the presence of CD4 T cells. We are investigating the kinetics of the antigen-specific CD4+ T cell response to various bacterial proteins expressed at different phases during the infection. We also have a great interest in the role of various professional antigen-presenting cells (APCs) throughout the infection and how they might dictate the helper T cell response to the infection. My previous work has shown that there are different roles for antigen presentation to helper T cells by APCs in non-lymphoid tissue compared with those found in the lymph nodes that drain that tissue. It will be interesting to determine if this dichotomy exists at different times during a chronic Salmonella infection and what role this might play in the “stalemate”. Lastly, we are interested in uncovering new helper T cell epitopes from Salmonella and other pathogens that will aid in development of vaccines that can better prime helper T cell responses. Because an individual population of helper T cells specific for a particular pathogenic antigen is so rare in the total T cell population, we are using soluble peptide-MHCII tetramers combined with a magnetic bead enrichment strategy pioneered in the laboratory of Marc Jenkins. This allows us to observe the full range of helper T cell immune responses from the initial naïve T cell population well into the immunologic memory phase.
Education
Appalachian State University
Duke University
University of Minnesota
Accomplishments
AAI Student Travel Grant for doctoral student
2014
Nominated as Pew Scholar
2010
Nominated as Searle Scholar
2010
AAI Student Travel Grant for doctoral student
2015
AAI Early Career Faculty Travel Grant
2013
AAI Student Travel Grants for two doctoral students
2013
Articles
Parenteral immunization with double-mutant heat labile toxin engages CD103+ dermal dendritic cells and redirects T cell immunity to the gut mucosa. (MUC4P.833)
2014
The vast majority of infectious agents enter hosts through mucosal compartments. Despite this, most current vaccines are administered via parenteral injection, which induce vigorous systemic but only limited mucosal immune responses. Studies have suggested that certain adjuvants can induce mucosal antibody responses regardless of route; however, there is minimal evidence that these injections direct antigen-specific effector T cells to the mucosa, where they are likely needed for protection against mucosal pathogens. We sought to explore the potential of the mucosal adjuvant dmLT (double-mutant heat-labile toxin) to drive antigen-specific T cells to the mucosa after parenteral immunization. By using a combination of peptide:MHCII-specific antibodies and tetramers, we can directly observe the impact of intradermal delivery of dmLT plus antigen, on both antigen-presenting cells (APCs) and antigen-specific T cells. Here we show that this immunization results in T cell upregulation of the gut mucosal homing marker, α4β7, in local draining lymph nodes and mucosal sites when compared to immunization with CpG. Additionally, we observed dmLT preferentially recruits skin CD103+ dendritic cells to the draining lymph nodes after parenteral immunization. These results show that administration of a mucosal adjuvant in the skin results in recruitment of mucosal-like APCs and induce T cell responses in remote, mucosal compartments.
Liver induced immunosuppression by Salmonella-specific CD4 T cells during persistent infection (P3097)
What role microenvironments play in dictating immune outcomes during infection is largely unknown. Our lab uniquely combines a murine model of persistent S. typhimurium infection with recombineered Salmonella strains and MHC-II tetramers to visualize endogenous Salmonella-specific CD4 T cell responses during infection in various organs. We hypothesize that an immunological stalemate between bacterial persistence and the host immune response is determined by anatomical location, which dictates T cell function and infection outcome. We show Salmonella-specific CD4 T cells adoptively transferred from lymphoid organs protect mice from subsequent challenge, while CD4 T cells transferred from infected livers increase susceptibility. Furthermore, lymphoid Salmonella-specific Th1-cells produce higher levels of interferon-γ, while FoxP3- liver CD4 T cells produce larger amounts of interleukin-10, with a decreased proliferative capacity. Additionally, we show lymphoid Th1 cells are potent activators of iNOS and reduce macrophage bacterial loads, while liver-derived Tr1-like cells fail to control bacterial replication, through attenuated iNOS activation. Whether these immunosuppressive Tr1-like cells are induced in the liver, or phenotypically switch upon entering the organ, remains under investigation. These results demonstrate that during persistent Salmonella infection different immunological responses occur at different anatomical sites, which may dictate the outcome of infection.
Parenteral immunization with double-mutant heat labile toxin engages CD103+ dermal dendritic cells and redirects T cell immunity to the gut mucosa. (MUC5P.751)
The majority of infectious agents enter via mucosal compartments. Despite this, most current vaccines are administered by parenteral injection, which induce limited mucosal T cell responses. It is known that certain adjuvants can induce mucosal antibody responses regardless of route; however, there is minimal evidence that these injections direct antigen-specific effector T cells to the mucosa, where they are likely needed for relevant protection. In the current study we examine the potential of dmLT (double-mutant heat-labile toxin), a detoxified adjuvant derived from the mucosal human pathogen enterotoxigenic Escherichia coli, to drive antigen-specific T cells to the intestinal mucosa after parenteral immunization. By using a combination of antibodies and tetramers specific for a known peptide:MHCII, we can track intradermal delivery of dmLT plus antigen, with regards to antigen-presentation and the antigen-specific CD4 T cell response. We show this immunization results in T cell upregulation of the gut mucosal homing marker, α4β7 in local draining lymph nodes, mucosal lymph nodes, colon, and small intestine when compared to immunization with CpG plus the same antigen. We also observed an increased frequency of CD103+ dendritic cells in response to dmLT administration that were presenting the injected antigen. Lastly, we determined that dmLT imparts a balanced Th1/Th17 cytokine response and is capable of providing protection against oral Salmonella typhimurium challenge.
Efficient generation of monoclonal antibodies against peptide in the context of MHCII using magnetic enrichment
Monoclonal antibodies specific for foreign antigens, auto-antigens, allogeneic antigens and tumour neo-antigens in the context of major histocompatibility complex II (MHCII) are highly desirable as novel immunotherapeutics. However, there is no standard protocol for the efficient generation of monoclonal antibodies that recognize peptide in the context of MHCII, and only a limited number of such reagents exist. In this report, we describe an approach for the generation and screening of monoclonal antibodies specific for peptide bound to MHCII. This approach exploits the use of recombinant peptide:MHC monomers as immunogens, and subsequently relies on multimers to pre-screen and magnetically enrich the responding antigen-specific B cells before fusion and validation, thus saving significant time and reagents. Using this method, we have generated two antibodies enabling us to interrogate antigen presentation and T-cell activation. This methodology sets the standard to generate monoclonal antibodies against the peptide–MHCII complexes.
Memory B cells contribute to rapid Bcl6 expression by memory follicular helper T cells
Follicular helper T (TFH) cells have emerged as the key cell type required for the formation of germinal centers and subsequent long-lasting antibody responses. It has been demonstrated that TFH cells enter the memory pool. However, it is unclear how the generation, survival, or activation of those TFH memory cells is regulated. Here we show that B-cell lymphoma 6 (Bcl6), a master regulator of TFH generation, is required for maintenance of TFH memory cells and subsequent humoral memory. In these recall responses, antigen-specific memory B cells majorly contribute to the quick induction of Bcl6 in TFH memory cells. Our results reinforce the importance of cognate interaction between memory TFH and memory B cells and give important implications for development of better vaccines.
