BACKGROUND: Treatment with methotrexate (MTX) in patients with rheumatoid 
arthritis (RA) leads to decreased total immunoglobulin (Ig) levels and impairs 
vaccine-specific IgG antibody levels following pneumococcal vaccination. The 
mechanisms by which MTX exerts these effects in RA are unknown. We aimed to 
evaluate whether MTX reduces vaccine-specific serum Ig levels and their 
functionality in RA patients following vaccination with pneumococcal conjugate 
vaccine, and if numbers of antigen-specific circulating plasmablasts are 
affected.
METHODS: Ten patients with RA on MTX and 10 RA patients without disease 
modifying anti-rheumatic drug (DMARD) were immunized with a dose 13-valent 
pneumococcal conjugate vaccine (Prevenar13). Circulating plasmablasts producing 
total IgG and IgA as well as specific IgG and IgA against two pneumococcal 
capsular serotypes (6B and 23F) were enumerated using ELISPOT 6days after 
vaccination. IgG levels against both these serotypes were determined with ELISA 
before and 4-6weeks after vaccination. Positive antibody response was defined as 
⩾2-fold increase of pre-vaccination antibody levels. The functionality of 
vaccine specific antibodies to serotype 23F was evaluated by measuring their 
ability to opsonize bacteria using opsonophagocytic assay (OPA) in 4 randomly 
chosen RA patients on MTX and 4 RA patients without DMARD.
RESULTS: After vaccination, RA patients on MTX showed significant increase in 
pre- to postvaccination antibody levels for 6B (p<0.05), while patients without 
DMARD had significant increases for both 6B and 23F (p<0.05 and p<0.01, 
respectively). Only 10% of RA on MTX and 40% of RA patients without DMARD showed 
positive post-vaccination antibody responses for both serotypes. Increased 
opsonizing ability after vaccination was detected in 1 of 4 RA patients on MTX 
and 3 of 4 patients on RA without DMARD. However, numbers of circulating total 
and vaccine-specific IgG- or IgA-producing plasmablasts did not differ between 
RA patients with or without MTX.
CONCLUSIONS: MTX treatment in RA leads to reduced vaccine-specific antibody 
responses and their functionality compared to untreated RA following 
pneumococcal vaccination using polysaccharide-protein conjugate vaccine. 
However, since there was no reduction in numbers of circulating total or 
vaccine-specific antibody-producing plasmablasts after vaccination this effect 
is probably not due to reduced activation of B cells in lymphoid tissue.
CLINICAL TRIAL REGISTRATION: NCT02240888.