Keksalarda immunitet pasayishining sabablari, jumladan timus bezining faoliyatining susayishi, T-hujayralar ishlab chiqarishning kamayishi, yallig'lanish jarayonlari, surunkali kasalliklar, D vitamini yetishmasligi, ovqatlanish muvozanatining buzilishi, spirtli ichimliklar va chekishning ta'siri