“…In the vast majority of cases it is caused by microbes commonly inhabiting the human body which, as a result of weakened immune reactions, cause the so-called opportunistic infections [8]. Apart from the tendency of recurrent infections, immunodeficiency is also accompanied by other health problems such as allergic phenomena [9], autoimmune phenomena [10,11], granulomas [12], tumors [13,14], endocrine disorders [15,16], and various cytopenias (most often thrombocytopenia [17] and neutropenia [18,19]) as well as diseases of the lungs [20] and gastrointestinal tract [21] (e.g., irritable bowel syndrome) [22,23]. Due to the underlying causes of immunodeficiencies, we can divide them into two groups: Primary Immunodeficiencies (PID), which are genetically determined and associated with mutations that are either inherited or appear de novo and Secondary Immunodeficiencies (SID), which are caused by external factors or the presence of comorbid disease [24,25].…”