analysis of differences in lymphocyte subsets and cd4+ t cells immune activation between re-detectable positive and non-re-detectable positive covid-19 convalescent patients

Background: when coronavirus disease 2019 (covid-19) first broke out, much literature was reported on the re-detectable positive phenomenon of covid-19 patients during recovery; however, there were few studies on the lymphocyte subsets, t-lymphocyte activation indicators, and levels of specific antibodies between the re-detectable positive (rp) and non-re-detectable positive (nrp) patients. objectives: this study aimed to analyze the immunological characteristics of rp and nrp patients among convalescent patients from post-discharge covid-19 patients and to explore immunological factors related to rp. methods: anticoagulated whole blood samples were collected from 11 healthy controls (hcs) and 66 covid-19 convalescent patients. then, the percentage of lymphocyte subsets and cd4+cd38+/hla-dr+ t cells were tested with flow cytometry, severe acute respiratory syndrome coronavirus 2 (sars-cov-2) anti-spike protein receptor-binding domain immunoglobulin g (s-rbd-igg) antibody was detected by chemiluminescence. results: b cells (%) in the rp group were significantly lower than that in the hc group (p = 0.014), and b cells (%) decreased successively in hc, nrp, and rp groups, with significant differences among the three groups (p = 0.016). cd3+ and cd8+ t cells (%) in the rp group were noticeably higher than that in the nrp group (p = 0.004 and 0.019, respectively); nevertheless, there was no difference in cd4+ t cells (%) and natural killer (nk) cells (%) among the three groups. the cd4+cd38+ and cd4+hla-dr+ t cells (%) in the rp group were noticeably higher than that in the hc group (p = 0.013 and 0.025). the analysis of differences among the three groups showed that cd4+cd38+ and hla-dr+ t cells (%) were also significantly different (p = 0.037 and 0.015), and cd4+hla-dr+ t cells (%) in the three groups increased in turn. meanwhile, there was a positive correlation between rbd-igg titer and cd4+hla-dr+ (%) (p = 0.003, r = 0.517), and the rbd-igg titer of hla-dr+ high group was higher than that of hla-dr+ low group (p = 0.005) in the covid-19 convalescent patients. conclusions: in this study, the immunological characteristics of the rp patients of covid-19 convalescent patients were analyzed based on the lymphocyte subsets and the relationship between s-rbd-igg and activated cd4+ t cells. the results showed that the low b cells (%) and the increased cd4+hla-dr+ t cells (%) in the convalescent patients of covid-19 might be related to the rp phenomenon, and the activated cd4+ t cells might play a crucial role in specific antibody responses.