Brief Deﬁnitive Report Rapid Cytotoxic T Lymphocyte Activation Occurs in the Draining Lymph Nodes After Cutaneous Herpes Simplex Virus Infection as a Result of Early Antigen Presentation and Not the Presence of Virus Scott N. Mueller,1 Claerwen M. Jones,1 Chris M. Smith,2 William R. Heath,2 and Francis R. Carbone1 1Department of Microbiology and Immunology,The University of Melbourne, Parkville,Victoria, 3010,Australia 2Immunology Division,The Walter and Eliza Hall Institute of Medical Research, Parkville,Victoria, 3050,Australia Abstract Localized cutaneous herpes simplex virus type 1 (HSV-1) infection leads to arming and initial expansion of cytotoxic T lymphocytes (CTLs) in the draining popliteal lymph nodes (PLNs) followed by migration and further proliferation in the spleen. To accurately characterize the se- quence of events involved in the activation and generation of anti-HSV CTLs, we used T cell receptor (TCR) transgenic mice specific for the immunodominant epitope from HSV glyco- protein B (gB498–505). We describe the detection of the initiation of antigen presentation in the draining lymph nodes by 4–6 h after infection with HSV-1. Analysis of CD69 up-regulation revealed activation of gB-specific CD8 T cells by 6–8 h after infection. Furthermore, we show that T cell proliferation begins no sooner than 24 h after activation and is marked by the concurrent appearance of CTL activity in the PLNs. These events are not dependent on the presence of virus in the draining lymph nodes, and suggest a requirement for recruitment of professional antigen-presenting cells to the site of T cell activation. Consequently, we have de- fined the initiation of the CD8 T cell–mediated response to cutaneous HSV-1 infection, dem- onstrating that the immune response to localized viral infection depends only on the appearance of cells presenting virus-derived antigen and commences with remarkable swiftness. Key words: CD8 T lymphocyte • HSV • TCR transgenic mice • antigen presentation • CFSE Introduction Efficient initiation of the adaptive immune response upon viral infection is essential to combat a rapidly replicating in- fectious pathogen. The immune system must be able to re- spond swiftly while maintaining a high degree of specificity toward the foreign organism. Two of the most important factors limiting the rapidity of the immune response soon after infection are the availability of professional APCs pre- senting viral antigens and their access to specific T lympho- cyte precursors in the lymphoid organs draining the site of infection. During localized infection, APCs are thought to Address correspondence to Francis R. Carbone, Department of Microbi- ology and Immunology, The University of Melbourne, Parkville, Victo- ria, 3010, Australia. Phone: 61-3-8344-9923; Fax: 61-3-9347-1540; E-mail: fcarbone@unimelb.edu.au and William R. Heath, Immunology Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria, 3050, Australia. Phone: 61-3-9345-2482; Fax: 61-3- 9347-0852; E-mail: heath@wehi.edu.au acquire viral antigens within infected tissues and migrate to the draining lymphoid tissue where they activate naive T cells (1). While the migration of professional APCs has been carefully examined after contact sensitization (2), it remains unclear how long such migration and antigen transport takes after immunization with an infectious agent. The adaptive immune response to cutaneous footpad HSV-1 infection peaks in the draining popliteal lymph nodes (PLNs) 5 d after infection (3–5). By this time, there has been a considerable proliferation of CTLs specific for the immunodominant epitope from HSV glycoprotein B (gB498–505) which is followed by migration and further ex- pansion of this population in the spleen. At the peak of the response, as many as 5% of the CD8 T cells in the PLNs and 10% in the spleen are specific for this determinant (5). Previous work has estimated the frequency of naive virus- specific CTL precursors in the mouse to be in the range of 651 J. Exp. Med.  The Rockefeller University Press • 0022-1007/2002/03/651/06 $5.00 Volume 195, Number 5, March 4, 2002 651–656 http://www.jem.org/cgi/content/full/195/5/651