2.1. Materials and Preparation of Egg Yolk Protein Extract

Roswell Park Memorial Institute (RPMI) 1640 medium and fetal bovine serum (FBS) were purchased from HyClone Laboratories, Inc. (Logan, MI, USA). Penicillin–streptomycin was purchased from Gibco-BRL (Grand Island, NY, USA). Lipopolysaccharide (LPS) and concanavalin A (ConA) were purchased from Sigma-Aldrich Co. (St. Louis, MO, USA). Murine ELISA kits for cytokine analysis were purchased from Bio Biosciences Co. (San Diego, CA, USA), while kits for immunoglobulin analysis were purchased from Immunology Consultants Laboratory Inc., (Portland, OR, USA). All other chemicals and reagents were purchased from Sigma-Aldrich Co.

The degreased egg yolk protein powder used in this study was obtained from Join Co. (Yongin, Korea). Egg yolk protein powder was extracted with water (EYW). Briefly, the EYW was extracted using an autoclave (DW-AC-131, Dong Won Scientific Co., Seoul, Korea) at 121 °C and 1.5× atmospheric pressure for 15 min by adding 100 mL of distilled water to 5 g of egg yolk protein powder. The solution was centrifuged at 1000× g for 10 min, after which the supernatant was freeze-dried for 3 days and stored at −20 °C until use.