Protection against Pertussis in Humans Correlates to Elevated Serum Antibodies and Memory B Cells

Abstract

Pertussis is a respiratory infection caused by Bordetella pertussis that may be particularly severe and even lethal in the first months of life when infants are still too young to be vaccinated. Adults and adolescents experience mild symptoms and are the source of infection for neonates. Adoptive maternal immunity does not prevent pertussis in the neonate. We compared the specific immune response of mothers of neonates diagnosed with pertussis and mothers of control children. We show that women have pre-existing pertussis-specific antibodies and memory B cells and react against the infection with a recall response increasing the levels specific serum IgG, milk IgA, and the frequency of memory B cells of all isotypes. Thus, the maternal immune system is activated in response to pertussis and effectively prevents the disease indicating that the low levels of pre-formed serum antibodies are insufficient for protection. For this reason, memory B cells play a major role in the adult defense. The results of this study suggest that new strategies for vaccine design should aim at increasing long-lived plasma cells and their antibodies.

Keywords: immune system; memory B cells; pertussis; sIgA; vaccination.

Figure 1

Anti-PT-specific Ig in the serum. (A,B) The plot shows the concentration of specific anti- pertussis toxin-specific IgG (PT-IgG) or pertussis toxin-specific IgA (PT-IgA) in the serum of control [healthy controls (HC) and lower respiratory tract infections (LRTI)] and PERTUSSIS mothers. (C) The plot shows the concentration of specific anti-PT-IgA in the serum of PERTUSSIS mothers with anti-PT-IgG ≥ 100 IU/mL or with anti-PT-IgG < 100 IU/mL. (D) Optical density value of IgM in the serum of control (HC and LRTI) and PERTUSSIS mothers. Statistical significance was determined using the Mann–Whitney test; *p < 0.05, **p < 0.01, and ***p < 0.001. A total of 50 HC, 17 LRTI, and 57 PERTUSSIS samples could be evaluated for IgG. A total of 15 HC, 15 LRTI, and 20 PERTUSSIS samples could be evaluated for IgA and IgM.

Figure 2

Peripheral B-cell subset analysis. (A) Frequency (%) of B cells (defined as CD19⁺), total memory B cells (CD19⁺CD27⁺), IgM (CD19⁺CD27⁺IgM⁺), and switched (CD19⁺CD27⁺IgM⁻) memory B cells is depicted for healthy controls (HC), lower respiratory tract infections (LRTI), and PERTUSSIS mothers. The staining was performed using antibodies anti-CD19, -CD24, -CD27, and -IgM. (B) A number of total IgM, IgA, and IgG spots per million of total peripheral blood mononuclear cells are shown both for control (HC and lower respiratory tract infections) and PERTUSSIS mothers. A total of 61 HC, 36 LRTI and 47 PERTUSSIS mothers were compared. Mann–Whitney statistical test was used for calculation of the reported p-value. Statistical significance is marked as *p < 0.05.

Figure 3

Memory B cells specific for pertussis antigens. (A,B,C) Number of specific anti-PT (toxin [PT], filamentous hemagglutinin [FHA], and pertactin [PRN])-IgG, -IgA, and -IgM spots per million of total cultured peripheral blood mononuclear cells are shown in healthy controls (n = 61), lower respiratory tract infections (n = 36), and PERTUSSIS (n = 47) mothers. Statistical significance was determined using the Mann–Whitney test; *p < 0.05, **p < 0.01, and ***p < 0.001.

Figure 4

IgA in breast milk reacts with several bacterial species. Graphs show the frequency of bacteria of the indicated species binding to IgA contained in the milk (1:10 dilution) of healthy controls (HC), lower respiratory tract infections (LRTI), and PERTUSSIS mothers. The difference between groups was determined using the Mann–Whitney test; **p < 0.01 and ***p < 0.001. Milk from 61 HC, 21 LRTI, and 53 PERTUSSIS mothers was analyzed for binding to B. pertussis, and 24 HC, 21 LTR and 28 PERTUSSIS samples were tested against all other bacteria.