Assessment of markers of the cell-mediated immune response after influenza virus infection in frail older adults

Abstract

The purpose of this study was to determine whether measures of the cell-mediated immune response to influenza virus could be used as markers of influenza virus infection. We studied 23 subjects who developed upper respiratory, lower respiratory, or systemic symptoms during a small outbreak of influenza in a nursing home population. Influenza virus culture from nasopharyngeal swabs yielded influenza virus isolates from 7 of the 23 subjects. Only three of the subjects had a fourfold rise in antibody titer to the influenza virus antigen positivity after the infection. Granzyme B and cytokine levels were measured in peripheral blood mononuclear cells (PBMC) obtained from all subjects and stimulated with live influenza virus. Elevated granzyme B levels in virus-stimulated PBMC in combination with lower respiratory tract or systemic symptoms in study subjects was a significant predictor of culture-confirmed influenza virus infection compared to those from whom influenza virus could not be identified. Cytokine levels did not distinguish between the two groups in a similar type of analysis. Granzyme B in combination with the clinical profile of symptoms may be a useful retrospective marker for influenza virus infection.

FIG. 1

Changes in titers of antibodies to each of the three strains of virus contained in the 1994-1995 influenza virus vaccine are shown. Represented are the individual fold increases in antibody titers for the influenza virus culture-negative (○) and culture-positive (•) groups. Shown are results for the response to influenza virus vaccination and the acute- to convalescent-phase period of the influenza outbreak.

FIG. 2

Individual antibody titers at each of the time points in the study are shown. Influenza virus culture-negative (○) and culture-positive (•) results were used to calculate the fold increases in antibody titers shown in Fig. 1.

FIG. 3

Granzyme B levels in individual PBMC lysates prepared after stimulation of the cultures with A/Texas/36/91 or A/Shangdong/09/93 are represented by the open circles (○). Aspase units reflect the colorimetric change as a result of granzyme B substrate cleavage. Results for influenza virus culture-positive (pos) and culture-negative (neg) subjects are shown. The median granzyme B levels (⧫) are shown, and error bars represent 95% confidence intervals. The difference between the two groups in A/Texas-stimulated cultures was just below statistical significance (P = 0.058).

FIG. 4

IL-2 levels measured in individual PBMC supernatants (○) after stimulation with either A/Texas/36/91 or A/Shangdong/09/93. Results for culture-positive (pos) and culture-negative (neg) subjects are shown. The median IL-2 levels (⧫) for each subset are shown, and error bars represent 95% confidence intervals.

FIG. 5

IFN-γ levels measured in individual PBMC supernatants (○) after stimulation with either A/Texas/36/91 or A/Shangdong/09/93. Results for culture-positive (pos) and culture-negative (neg) subjects are shown. The median IFN-γ levels (⧫) for each subset are shown, and error bars represent 95% confidence intervals.

FIG. 6

IL-10 levels measured in individual PBMC supernatants (○) after stimulation with either A/Texas/36/91 or A/Shangdong/09/93. Results for culture-positive (pos) and culture-negative (neg) subjects are shown. The median IL-10 levels (⧫) for each subset are shown, and error bars represent 95% confidence intervals.