[Show abstract][Hide abstract] ABSTRACT: Ab production is critical for antimicrobial immunity, and the initial step in this process is the binding of Ag to the BCR. It has been shown that small soluble proteins can directly access the lymph node follicles to reach naive B cells, but virus particles must be translocated into follicles via subcapsular sinus macrophages. In this article, we explore how large particulate Ags generate humoral immune responses. Ag-specific follicular B cells rapidly acquired Ag, presented peptide:MHC class II ligands, and produced T-dependent Ab responses following s.c. injection of 1-mum, Ag-linked microspheres, despite the microspheres being confined to the subcapsular sinus. The mechanism of Ag acquisition did not require dendritic cells, subcapsular sinus macrophages, or B cell movement to the subcapsular sinus. Rather, B cell Ag acquisition was protease-dependent, suggesting that some protein Ags are cleaved from the surface of particles to directly initiate humoral immune responses.
Full-text · Article · Mar 2010 · The Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: Effector (Teff) and regulatory (Treg) T cells produce cytokines that balance immunity and immunopathology at sites of infection. It is not known how this balance is achieved. Here, we show that Treg and Teff cells specific for the same foreign peptide:major histocompatibility complex II (pMHCII) ligand accumulated preferentially in a subcutaneous site injected with the relevant antigen plus an adjuvant. Some of the Treg cells in this site were producing IL-10 12 days after injection, whereas a similar fraction of the Teff cells were producing IFN-gamma. Acute ablation of Treg cells increased the fraction of IFN-gamma-producing Teff cells, indicating that Teff function was limited by the Treg cells. Production of cytokines by both populations was driven by pMHCII presentation by local CD11b(hi) dermal dendritic cells. Therefore, balanced production of microbicidal and suppressive cytokines in inflamed skin is achieved by simultaneous dendritic cell antigen presentation to Teff and Treg cells.
[Show abstract][Hide abstract] ABSTRACT: To investigate the role of TCR signaling in the exit of CD4+ T cells from cell cycle, we took advantage of a low frequency TEa T cell adoptive transfer technique as well as the Y-Ae mAb to interrupt Ag/MHC recognition before the completion of clonal expansion. Termination of TCR signaling after 36 h of Ag exposure caused an immediate reduction in cell size and deceleration of G1->SG2M phase cell cycle progression. As a consequence, clonal expansion in the absence of durable TCR signaling decreased by two-thirds. Thus, CD4+ T cells scan for the presence Ag throughout their clonal expansion response, and continuously adjust their rate of cell growth and G1->S phase transition to match their intensity of TCR signaling.
Full-text · Article · Jan 2008 · The Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: The initial step in a humoral immune response involves the acquisition of antigens by B cells via surface immunoglobulin. Surprisingly, anatomic studies indicate that lymph-borne proteins do not have access to the follicles where naive B cells reside. Thus, it is unclear how B cells acquire antigens that drain to lymph nodes. By tracking a fluorescent antigen and a peptide:MHC II complex derived from it, we show that antigen-specific B cells residing in the follicles acquire antigen within minutes of injection, first in the region closest to the subcapsular sinus where lymph enters the lymph node. Antigen acquisition, presentation, and subsequent T cell-dependent activation did not require B cell migration through the T cell area or exposure to dendritic cells. These results indicate that the humoral response is initiated as soluble antigens diffuse directly from lymph in the subcapsular sinus to be acquired by antigen-specific B cells in the underlying follicles.
[Show abstract][Hide abstract] ABSTRACT: We explored the relationship between the time of naive CD4+ T cell exposure to antigen in the primary immune response and the quality of the memory cells produced. Naive CD4+ T cells that migrated into the skin-draining lymph nodes after subcutaneous antigen injection accounted for about half of the antigen-specific population present at the peak of clonal expansion. These late-arriving T cells divided less and more retained the central-memory marker CD62L than the T cells that resided in the draining lymph nodes at the time of antigen injection. The fewer cell divisions were related to competition with resident T cells that expanded earlier in the response and a reduction in the number of dendritic cells displaying peptide-major histocompatibility complex (MHC) II complexes at later times after antigen injection. The progeny of late-arriving T cells possessed the phenotype of central-memory cells, and proliferated more extensively during the secondary response than the progeny of the resident T cells. The results suggest that late arrival into lymph nodes and exposure to antigen-presenting cells displaying lower numbers of peptide-MHC II complexes in the presence of competing T cells ensures that some antigen-specific CD4+ T cells divide less in the primary response and become central-memory cells.
Full-text · Article · May 2006 · Journal of Experimental Medicine
[Show abstract][Hide abstract] ABSTRACT: Recently, static and dynamic imaging methods have produced the first glimpses of the interactions between antigen-specific T cells and peptide-MHC-bearing antigen-presenting cells in the lymph nodes. Using data from these experiments, we produced a numerically, spatially, and temporally scaled simulation of the first 50 hr of the primary T cell-dependent immune response. The simulation highlights how lymph node structure facilitates antigen presentation to rare, naive, antigen-specific CD4+ T cells.