Pulmonary influenza infection causes prolonged lymph node hypertrophy while processed viral antigens continue to be presented to virus-specific CD8 T cells. We show that naïve, but not central/memory, nucleoprotein (NP)-specific CD8 T cells recognized antigenbearing CD11b + DC in the draining lymph nodes more than 30 days after infection. After these late transfers, the naïve CD8 T cells underwent an abortive proliferative response in the mediastinal lymph node (MLN), where large clusters of partially activated cells remained in the paracortex until at least a week after transfer. A majority of the endogenous NP-specific CD8 T cells that were in the MLN between 30 and 50 days after infection also showed signs of a continuing response to antigen stimulation. A high frequency of endogenous NP-specific CD8 T cells in the MLN indicates that late antigen presentation may help shape the epitope dominance hierarchy during reinfection.

Increased nutrient inputs to temperate coastal waters have led to increased occurrences of macroalgal blooms worldwide. To identify nutrients that are limiting to macroalgae and to determine whether different forms of these nutrients and long-term ambient nutrient conditions affect macroalgal response, we used in situ enrichment methods and tested the response of 2 bloom-forming species of macroalgae, Ulva lactuca and Gracilaria tikvahiae, from shallow estuaries of Waquoit Bay, Massachusetts, USA, that receive different land-derived N inputs. We enriched caged macroalgal fronds with nitrate, ammonium, phosphate, and N + P combinations, and measured growth, nutrient content, and δ 15 N signatures of fronds after 2 wk of incubation. In these estuaries, P did not limit growth, however, the 2 species differed in growth response to N additions. Growth of U. lactuca was greater in Childs River (CR), the estuary with higher nitrate inputs, than in Sage Lot Pond (SLP); growth in SLP increased with nitrate and ammonium enrichment. In contrast, growth of G. tikvahiae was greater in SLP than in CR, but had no growth response to N enrichment in either site. C and N contents differed initially between species and sites, and after nutrient enrichment. Final tissue % N increased and C:N decreased after nitrate and ammonium enrichment. δ 15 N values of the macroalgae demonstrated uptake of the experimental fertilizers, and a higher affinity and faster turnover of internal N pools with ammonium than nitrate enrichment in both species. We suggest that U. lactuca blooms in areas with both high nitrate and ammonium water column concentrations, and is more N-limited in oligotrophic waters where DIN levels are too low to sustain high growth rates. G. tikvahiae has a greater N storage capacity than U. lactuca, which may allow it to grow in less nutrientrich waters.

Cytotoxic T lymphocytes are important targets for vaccines against a wide variety of infections that enter the body via mucosal tissues. To induce effective immunity these vaccines must include the most protective epitopes and elicit rapid recall responses at the site of infection. Although live attenuated viruses are sometimes used to induce cellular immunity against recurrent influenza infections, the mechanisms that determine the magnitude of the response to individual viral components are very poorly defined. Heterosubtypic infections in B6 mice illustrate an additional level of complexity, when the antigen-specificity of the response shifts dramatically between primary and secondary challenge. This model provides a unique opportunity to identify the mechanisms that regulate memory CD8 T cell reactivation in vivo and control the specificity of the recall response by pathogen-specific CTL. We show that multiple factors contribute to the changing pattern of immunodominance during secondary infection, including the location of the memory CD8 T cells at the time of reinfection and their ability to directly recognize migratory CD103+ DC as they arrive in the lung draining lymph node.

T cell mediated immunity to influenza infection disappears within a few months, even though large numbers of virus-specific memory CD8 T cells remain in the circulation for at least two years. It has been suggested that antigen persistence may play an instrumental role in protective cellular immunity. This idea is supported by the presence of activated virus-specific CD8 T cells in the respiratory tract during the months following infection, when processed influenza antigens are presented to virus-specific CD8 T cells in the draining lymph nodes. A majority of the endogenous virus-specific CD8 T cells that were at the mucosal surface of the lungs one month after infection expressed both CD69 and CD103. In contrast, bystander memory CD8 T cells that entered the lungs during parabiosis did not acquire this phenotype. We have crossed CD69KO and CD103KO mice with F5 TcR transgenic mice which are specific for the influenza NP peptide. Transfer studies show that CD103-deficiency results in reduced numbers of CD69+ NP-specific CD8 T cells in the lungs. In contrast, CD69-deficiency results in slightly delayed T cell activation followed by a late accumulation of CD103-negative NP-specific CD8 T cells in the lung parenchyma. This work was supported by NIH grants AI065895 & AI071213 (LSC), RO1 AI-36532 (GH).

Influenza viruses encode four major epitopes (NP, PA, PB1 and PB2) that are recognized by naïve CD8 T cells in C57BL/6 mice. MHC class I tetramer analysis has shown that CD8 T cells specific for the NP and PA epitopes are equally represented during the response to a primary infection with the reassortant HKx31 influenza virus. Secondary challenge with the serologically distinct A/PR/8 strain, however leads to a change in the dominance hierarchy so that NP-specific cells outnumber PA-specific cells in most tissues by approximately 5:1. We recently found that processed NP antigen persists in vivo long after infectious influenza virus has been eliminated. Large numbers of endogenous NP-specific CD8 T cells in the antigen bearing lymph nodes showed signs of a response to recent antigen stimulation. In contrast, there were much smaller numbers of PA-specific CD8 T cells in the mediastinal lymph node (MLN), with a much lower frequency of activated T cells. Since DC carry viral antigens to the MLN immediately after influenza infection, we have investigated whether the local specificities of antigen-specific memory CD8 T cells in the MLN at the time of reinfection help shape the specificity of the recall response. Since there is evidence in the literature that NP epitope is more protective than PA epitope, these studies will help us to elucidate the role of antigen and the biology of local specific memory CD8 T cell response in the shaping of the CD8 T cell response during secondary infections with influenza virus. This work was supported by NIH grants AI065895 & AI071213 (LSC),