PJP is rarely described in patients with idiopathic CD4+ lymphocytopenia (ICL), a rare T-cell deficiency of unknown origin with persistently low levels of CD4+ T-cells (<300 μl−1 or <20 % of total lymphocytes) but repeated negative human immunodeficiency virus (HIV) tests. Here, CD4 is linked to idiopathic CD4 lymphocytopenia.