However, upon stratifying patients based on their immunological status, a noteworthy, statistically significant decrease in plasma C4a concentrations was observed in individuals with ME/CFS and immunodeficiencies (ME/CFS + ID) in contrast to those with ME/CFS but no immunodeficiencies (ME/CFS − ID) and the healthy control group (Figure 2B). Here, C4A is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.