3. Results
The Activation Induced Marker (AIM) assay revealed circulating memory
Tfh (cTfh) cells responded better to the spike proteins of wild type
SARS-CoV2 virus compared to the delta strain in naïve vaccinees(Fig 1B-C, G) . There was no difference in cTfh response between
the spike proteins of the wild and delta strain in convalescent
vaccinees (Fig 1D-E, H) . The breadth of AIM response of cTfh
cells to delta spike protein was higher in convalescent vaccinees
compared to naïve vaccinees (Fig 1J) . The magnitude of response
to wild type spike protein did not show difference between the two
groups but both the groups responded to the wild type spike protein(Fig 1I) . We also observed an increase in central memory
compartment (CCR7+CD45RA-) in
CD4+ T cells in response to the Spike wild type
protein in infection naïve vaccinees (Fig K-L, O) while
convalescent vaccinees did not show any difference (Fig M-N,
P ). When we investigated the antigen specific cytokine response from
cTfh, both naive vaccinees and convalescent vaccinees showed higher
expression of IL-21 when stimulated with wild type spike protein than to
delta spike protein (Fig 2B-E, G-H) . But expression of IL-21
was significantly higher in naïve vaccinees compared to convalescent
vaccinees both for wild type and delta type, thought it was not
statistically significant for delta spike (Fig 2 I-J) . The
neuralization activity did not show any difference between naïve
vaccinees or convalescent vaccinees (Fig 2K) but it positively
correlated with IL-21 expression from cTfh cells from naïve vaccinees(Fig 2L-M) . Furthermore, our phenotyping of spike specific cTfh
from both the groups were biased towards cTfh2 phenotype which is
CXCR3-/CCR6- cells (Fig 2N-O).
Our multiplex data revealed that low level of inflammation was still
ongoing in these convalescent vaccinees as they displayed higher levels
of IL-6 and IL-1β compared to naïve vaccinees (Fig 3H-I) . On
the other hand, Tfh promoting cytokines like IL-21, IL-4 and IL-10(Fig 3A-C) and anti-viral memory response inducing cytokines
like IFN-γ, IL-15, IL-12(Fig 3D-F) were elevated in naïve vaccinees as compared to
convalescent vaccines. All the above data indicated that though cTfh
cells from convalescent vaccinees recognizes both wild type and delta
spike proteins, their response is low compared to naïve vaccinees.