Fish oil feeding enhances lymphocyte proliferation but impairs virus-specific T lymphocyte cytotoxicity in mice following challenge with influenza virus

Abstract

The effect of a fish oil diet on virus-specific cytotoxicity and lymphocyte proliferation was investigated. Mice were fed fish oil (17 g fish oil and 3 g sunflower/100 g) or beef tallow (17 g tallow and 3 g sunflower/100 g) diets for 14 days before intranasal challenge with influenza virus. At day 5 after infection, lung virus-specific T lymphocyte, but not macrophage or natural killer (NK) cell, cytotoxicity was significantly lower in mice fed fish oil, while bronchial lymph node cell proliferation to virus was significantly higher. In mice fed fish oil, spleen cell proliferation to virus was also significantly higher following immunization. The results showed that, despite improved lymphocyte proliferation, fish oil impairs primary virus-specific T lymphocyte cytotoxicity. This impairment may explain the delayed virus clearance that we have previously reported in infected mice fed the fish oil diet.

Fig. 1

Influenza virus-specific lung cytotoxic T cell activity in mice. The mice were fed diets containing fish oil (□) or beef tallow (▪) (20 g/100 g) for 14 days before intranasal challenge with A/Queensland influenza virus. Cytotoxic T cell activity was determined at 50:1 and 100:1 E:T ratios with influenza virus-infected P815 target cells. Values are mean specific lysis activity ± s.e.m. (n = 5/diet group) at day 5. *Significantly higher cytotoxic activity (P < 0.05).

Fig. 2

Proliferative response to influenza virus in mice infected or immunized with influenza. Mice were fed diets containing fish oil or beef tallow. Mice were killed at day 5 or day 12 after challenge with A/Queensland influenza virus. Mice immunized intraperitoneally were killed at day 14. Values are mean stimulation index (SI) ± s.e.m. (n = 20/group at day 5, n = 5/group at day 12). Bars not sharing common superscript letters are significantly different (P < 0.05). SI is calculated from (ct/min stimulated cells)/(ct/min control cells). Top panel, BLN stimulated with 10 haemagglutinin units (HA) influenza virus/ml (A) or 5 HA influenza virus/ml (B). Bottom panel, spleen cells stimulated with virus (10 HA/ml) or concanavalin A (Con A; 5 μg/ml). Data are mean ± s.e.m. (n = 10/diet group). *P < 0.05 compared with values from beef tallow diet group.