Descriptive evaluation of antibody responses to severe acute respiratory coronavirus virus 2 (SARS-CoV-2) infection in plasma and gingival crevicular fluid in a nursing home cohort-Arkansas, June-August 2020

Abstract

Objective: To characterize and compare severe acute respiratory coronavirus virus 2 (SARS-CoV-2)-specific immune responses in plasma and gingival crevicular fluid (GCF) from nursing home residents during and after natural infection.

Design: Prospective cohort.

Setting: Nursing home.

Participants: SARS-CoV-2-infected nursing home residents.

Methods: A convenience sample of 14 SARS-CoV-2-infected nursing home residents, enrolled 4-13 days after real-time reverse transcription polymerase chain reaction diagnosis, were followed for 42 days. After diagnosis, plasma SARS-CoV-2-specific pan-Immunoglobulin (Ig), IgG, IgA, IgM, and neutralizing antibodies were measured at 5 time points, and GCF SARS-CoV-2-specific IgG and IgA were measured at 4 time points.

Results: All participants demonstrated immune responses to SARS-CoV-2 infection. Among 12 phlebotomized participants, plasma was positive for pan-Ig and IgG in all 12 participants. Neutralizing antibodies were positive in 11 participants; IgM was positive in 10 participants, and IgA was positive in 9 participants. Among 14 participants with GCF specimens, GCF was positive for IgG in 13 participants and for IgA in 12 participants. Immunoglobulin responses in plasma and GCF had similar kinetics; median times to peak antibody response were similar across specimen types (4 weeks for IgG; 3 weeks for IgA). Participants with pan-Ig, IgG, and IgA detected in plasma and GCF IgG remained positive throughout this evaluation, 46-55 days after diagnosis. All participants were viral-culture negative by the first detection of antibodies.

Conclusions: Nursing home residents had detectable SARS-CoV-2 antibodies in plasma and GCF after infection. Kinetics of antibodies detected in GCF mirrored those from plasma. Noninvasive GCF may be useful for detecting and monitoring immunologic responses in populations unable or unwilling to be phlebotomized.

Fig. 1.

Distribution of plasma and GCF antibody responses to SARS-CoV-2 infection over time in a nursing home cohort—Arkansas, June–August 2020. Distribution of positive plasma pan-Ig (panel A), IgM (panel B), IgG (panel C), and IgA (panel D) antibody titers by the number of weeks since the first RT-PCR–positive result. Plasma titers ≥1:100 were considered positive. Distribution of positive GCF IgG (panel E) and IgA (panel F) ratios by the number of weeks from the first RT-PCR–positive result. GCF Ig ratios defined as SARS-CoV-2 specific Ig/total Ig are reported in ng/100 µg. The y-axes are plotted in logarithmic scale. Note. GCF, gingival crevicular fluid; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; RT-PCR, real-time reverse-transcription polymerase chain reaction.

Fig. 2.

Plasma and GCF antibody responses in relation to RT-PCR and viral culture results in individual participants with SARS-CoV-2 infections in a nursing home cohort—Arkansas, June–August 2020. (Top panels) Composite RT-PCR results were determined from oropharyngeal, anterior nasal, and saliva specimens collected at each evaluation visit. If any respiratory or saliva specimen obtained from a participant at a given visit was RT-PCR positive, that participant was considered RT-PCR positive on that day. If all respiratory and saliva specimens obtained from a participant at a given visit were RT-PCR negative, that participant was considered RT-PCR negative on that day. Respiratory specimens with a RT-PCR Ct ≤34 were submitted for viral-culture testing. Due to challenges with specimen collection, transport, and processing, RT-PCR results for each specimen type were not always available for each visit. (Middle panels) Plasma pan-Ig (purple), IgG (green), IgA (blue), and IgM (orange) antibodies were considered positive with titers ≥1:100. Neutralization (black dashed) antibodies were considered positive with titers ≥1:80. Filled circles indicate a positive result, open circles indicate negative results, and asterisks indicate specimens were not tested. The y-axis is plotted in logarithmic scale. (Bottom panels) GCF IgG (green) and IgA (blue) antibodies are reported as GCF ratios in ng/100 µg and represent SARS-CoV-2 specific Ig/total Ig. Filled circles indicate a positive result, open circles indicate negative results, and asterisks indicate specimens were not tested. The y-axis is plotted in logarithmic scale. Note. GCF, gingival crevicular fluid; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; RT-PCR, real-time reverse-transcription polymerase chain reaction; Ct, cycle threshold. All data shown in days since the first RT-PCR positive result.