High Titer of Antibody Against Pneumococcal IgA1 Protease in Healthy Individuals

Mina Gholami1, 2, Davoud Afshar1, *, Mozhgan Kheirandish1, Farzaneh Rafiee1, Reza Ranjbar3, Amir Hasanzadeh4
1 Department of Microbiology, Zanjan University of Medical Sciences, Zanjan, Iran
2 Student Research Committee, Zanjan University of Medical Sciences, Zanjan, Iran
3 Molecular Biology Research Center, Systems Biology and Poisonings Baqiyatallah University of Medical Sciences, Tehran, Iran
4 Department of Microbiology, Maragheh University of Medical Sciences, Maragheh, Iran

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© 2020 Gholami et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Department of Microbiology, Zanjan University of Medical Sciences, Zanjan, Iran; Tel: +982433140297; E-mail:


Background and Objectives:

Considering rising antibiotic resistance in various strains of Streptococcus pneumoniae, there is a need to find new immunogenic candidates for developing pneumococcal vaccines. Immunoglobulin A1 (IgA1) protease is one of the virulence factors playing an important role in the pathogenesis of S. pneumoniae infections. In the present study, we aimed to evaluate the titer of antibody against pneumococcal recombinant IgA1 protease in the serum of healthy humans.

Materials and Methods:

A part of the IgA1 protease gene (705 bp) from S. pneumonia ATCC 49619 was amplified by PCR and then digested using restriction enzymes and ligated by the pET28a expression vector. The recombinant protein was expressed in E. coli BL21 strain. Affinity chromatography was used to purify the protein. The titer of antibody against the recombinant protease was determined in healthy individuals in three age groups of <2, 2-40, and > 40 years using indirect Enzyme-Linked Immunosorbent Assay (ELISA).


The expression and purification of the IgA1 recombinant protease were successful. The concentration of the purified protein was determined as 1.013 mg/ml using the NanoDrop method. The titer of anti-recombinant IgA1 protease antibody (20, 40, 80 and 160) showed a significant correlation with age (p-value<0.05). According to our results, the antibody titer was desirable, especially in individuals over two years old.


In the present study, desirable antibody titers against the pneumococcal recombinant IgA1 protease were seen in the three groups’ serum of healthy individuals. However, a significant correlation was not totally observed among groups.

Keywords: IgA1 protease, Streptococcus pneumoniae, Vaccine candidate, IgA1 protease, NanoDrop method, Pneumococcal surface protein A (PspA).