similar findings. By contrast, Lee et al. (1999) found that IR strain RB51, with or without IL-12 as an adjuvant, did not protect against strain 2308 challenge. These conflicting results could possibly be explained based on the fact that other groups stimulated for 24 h while we stimulated for 4 h. Mechanistically, some of these differences between HK vs. IR vs. live strains in induced DC and T-cell function and protection could be due to the amount and nature of antigen being processed and presented as well as the extent to which DCs are stimulated. In a different model, the findings of Kalupahana et al. (2005) using HK and live Salmonella typhimurium supported the above premise by showing that prolonged contact with HK bacteria was necessary to obtain similar DC activation and function achieved by live strains in a shorter period. Additionally, in contrast to the 65 °C, 30 min of heat inactivation by Vemulapalli and colleagues (Sanakkayala et al., 2005), selleck we used a higher temperature of 80 °C for 1 h. Theoretically, although
not likely, additional heating may have disrupted the Brucella cell envelopes (Barquero-Calvo et al., 2007) and exposed large amounts of Brucella lipopolysaccharide, lipoproteins, peptidoglycan, DNA and other molecules recognized by innate immunity. Additional differences between IR and HK could be due to the fact that IR may stimulate a better DC-mediated CD8 response than HK (Datta et al., 2006). Besides differences in the ability of IR vs. HK to stimulate more CD8- vs. CD4-mediated learn more immune responses, and the role of IR vs. HK in protection, DC function is also regulated by TNF-α, IL-12 and IL-10. As stated previously,
TNF-α production is critical for maximal IL-12 production and CD4 Th1 response. If either is decreased, DC-mediated T-cell responses and potentially protection could be decreased. Another mechanism by which protection would be decreased would be through an IL-10-mediated T-regulatory response that would downregulate IL-12 production by DCs (Huang et al., 2001; McGuirk et al., 2002). Correspondingly, HK and/or IR strains may suboptimally stimulate BMDCs at a given dose, which might induce them to become tolerogenic DCs (semi-mature DCs) with the inability to produce proinflammatory cytokines (Lutz & Schuler, all 2002). As others have shown that both HK and IR strains of B. abortus induced similar levels of IL-10 (Sanakkayala et al., 2005), we did not determine the ability of HK or IR strains to induce IL-10 secretion from BMDCs. However, it is possible that live vs. HK or IR strains may induce different levels of IL-10 that could influence DC and T-cell function and protection. Thus, our findings, along with already published studies, suggest multiple mechanisms for differences between live vs. IR vs. HK strain-induced DC function, T-cell function and protection. Additional studies are warranted to further investigate these mechanisms as well as their impact on protection.