Abstract: This study aimed to assess the potential effect of casein glycation via the Maillard reaction on in vivo immunoenhancing efficacy of tryptic casein digest in immunosuppressed mice. Glycated casein was prepared by the Maillard reaction of casein with lactose. Glycated and native casein were digested with trypsin to generate glycated casein digest and casein digest, respectively. Mice were treated with cyclophosphamide at 80 mg/kg mb for 3 days to induce immunosuppression, and then were given the two digests, separately at dose levels of 100, 200, and 400 mg/kg mb for 25 days. Afterwards, immune organ (spleen and thymus) indices, serum biochemical indices, immunoglobulin (IgM, IgA, and IgG) levels, lymphocyte proliferation capacity, and natural killer (NK) cell viability were evaluated. Results indicated that the immune status of mice in the model group was lower than that in the control group treated with normal saline as manifested by a significant decrease in immune organ indices, serum biochemical indices, serum Ig levels, spleen lymphocyte proliferation index and NK cell viability (P < 0.05). Compared with the immunosuppressed mice, spleen and thymus indices, serum IgM, IgA and IgG levels, spleen lymphocyte proliferation index, and NK cell viability increased by 35.9%–66.4%, 50.5%–62.9%, 21.6%–30.4%, 27.1%–41.8%, 37.2%–45.1%, 34.2%–51.1%, and 32.1%–90.7% in the mice treated with casein digest at the medium and high doses, and by 27.7%–51.9%, 39.2%–52.6%, 19.1%–29.0%, 21.8%–35.3%, 30.1%–41.6%, 32.9%–41.6%, and 27.3%–81.1% in the mice treated with glycated casein digest at the medium and high doses, respectively. Both digests were able to attenuate the decrease in immune indices of immune suppressed mice induced by cyclophosphamide, while casein digest showed higher immuno enhancing efficacy than glycated casein digest. Therefore, casein glycation via the Maillard reaction could decrease the immunoenhancing activity of its tryptic digest on mice.

Key words: casein, Maillard reaction, glycation, mice, immunoenhancing effect