The paper by Pawelek et al. [1] discussed the roles of both adaptive and innate immune responses in response to influenza infection. While the model was based on the innate immune response by type I interferon, it was mentioned that other cytokines might also be involved.

I would like to point out that vitamin D makes important contributions to the innate response against type A influenza. The ultraviolet-B-vitamin D-influenza hypothesis was proposed by John Cannell and colleagues based on the seasonality of epidemic influenza [2]. The role of vitamin D in reducing risk of influenza was supported in a randomized controlled trial involving African-American women in the United States [3]. It was also supported by a randomized controlled trial involving school children in Japan [4]. An observational study found significantly reduced risk of acute respiratory infections for serum 25-hydroxyvitamin D concentrations above 38 ng/ml [5].

It was also found in an ecological study of the 1918-19 pandemic influenza that communities with higher solar UVB doses had lower influenza case-fatality rates [6]. The reasons for this finding were attributed to a reduced cytokine storm in response to the type AH1N1 infection as well as induction of cathelicidin to combat the ensuing bacterial infection.

The results from [1] might be extended through a model involving the effects of vitamin D.

Disclosure
I receive funding from the UV Foundation (McLean, VA), Bio-Tech Pharmacal (Fayetteville, AR), the Vitamin D Council (San Luis Obispo, CA), the Vitamin D Society (Canada), and the Sunlight Research Forum (Veldhoven).

References
1. Pawelek KA, Huynh GT, Quinlivan M, Cullinane A, Rong L, et al. (2012) Modeling within-host dynamics of influenza virus infection including immune responses. PLoS Comput Biol 8(6): e1002588. doi:10.1371/journal.pcbi.1002588
2. Cannell JJ, Vieth R, Umhau JC, Holick MF, Grant WB, et al. (2006) Epidemic influenza and vitamin D. Epidemiol Infect. 134(6):1129-40.
3.Aloia JF, Li-Ng M. (2007) Re: epidemic influenza and vitamin D. Epidemiol Infect. 135(7):1095-6; author reply 1097-8.
4. Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, et al. (2010) Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 91(5):1255-60.
5. Sabetta JR, DePetrillo P, Cipriani RJ, Smardin J, Burns LA, et al. (2010) Serum 25-hydroxyvitamin D and the incidence of acute viral respiratory tract infections in healthy adults. PLoS One. 5(6):e11088.
6. Grant WB, Giovannucci E. (2009) The possible roles of solar ultraviolet-B radiation and vitamin D in reducing case-fatality rates from the 1918–1919 influenza pandemic in the United States. Dermatoendocrinol. 1(4): 215-9.