Department of Microbiology and Immunology, University of California, Santa Cruz, Santa Cruz, CA 95064, USA.|Department of Microbiology and Immunology, University of California, Santa Cruz, Santa Cruz, CA 95064, USA.|Department of Microbiology and Immunology, University of California, Santa Cruz, Santa Cruz, CA 95064, USA.|Department of Microbiology and Immunology, University of California, Santa Cruz, Santa Cruz, CA 95064, USA.