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Immunosuppression is characterized by a dysfunction of humoral and/or cellular immune response leading to increase of susceptibility to secondary infections, increase of mortality and morbidity, poor productivity, and welfare and vaccination failures. Humoral immune response depression is due to perturbation of soluble factors, as complement and chemokines in innate immunity and antibodies or cytokines in adaptive immunity. At the cellular immune response, immunosuppression is the consequence of the dysfunction of T-cells, B-cells, heterophils, monocytes, macrophages, and natural Killer cells. Immunosuppression in turkeys can be caused by numerous, non-infectious, and infectious agents, having variable pathological and molecular mechanisms. Interactions between them are very complex. This paper reviews the common viruses inducing clinical and sub-clinical immunosuppression in turkeys, and enteric and neoplastic viruses in particular, as well as the interactions among them. The evaluation of immunosuppression is currently based on classical approach; however, new technique such as the microarray technology is being developed to investigate immunological mediator's genes detection. Controlling of immunosuppression include, in general, biosecurity practices, maintaining appropriate breeding conditions and vaccination of breeders and their progeny. Nevertheless, few vaccines are available against immunosuppressive viruses in turkey's industry. The development of new control strategies is reviewed. [ABSTRACT FROM AUTHOR]

Objective: During the Coronavirus Disease-2019 (COVID-19) pandemic, in addition to the current measures, the healthy immune system plays an essential role and various natural agents have been recommended to boost innate immunity. The aim of this study was to investigate any association between the potential immunomodulatory activity and drinking olive leaf tea (OLT) in the COVID-19 pandemic. Design: The study was conducted among the workers in a tractor factory where OLT was served in routine. Drinking at least one cup of OLT per day for a minimum of 1 month was the inclusion criteria used in the study. The workers who had a history of vaccination and COVID-19 were excluded from the study, and lymphocyte subsets, interleukin (IL)-2, IFN-γ, COVID-19-specific IgM and IgG levels were analyzed in all the participants to determine the asymptomatic individuals among the participants and compare the immunological parameters. Results: The study was conducted among 336 workers, 183 of them were OLT drinkers and 153 were OLT nondrinkers. The results showed higher values of CD3−/CD16/56 (natural killer [NK]) cells, CD3+/CD16/56 (natural killer T [NKT]) cells, total NK (NK+NKT) cells, and serum IFN-γ, and IL-2 levels in OLT drinkers compared to the nondrinkers. Although all the OLT drinkers and nondrinkers included in the study reported no history of COVID-19, specific COVID-19 IgG levels were found positive in 60% of OLT drinkers and 38% OLT nondrinkers. Conclusions: Peripheral NK and NKT cell values and IL-2 and IFN-γ secretion levels were found higher in the OLT drinking group. There were positive correlations between the OLT drinking frequency and NK cell counts. Moreover, the number of individuals who had "asymptomatic" COVID-19 infection was higher in the OLT drinking group than in the nondrinking cohort. Clinical Trial Registration Number: The trial has been registered in the ClinicalTrials.gov database (CTR NCT05222347). [ABSTRACT FROM AUTHOR]