Compromised influenza virus-specific CD8(+)-T-cell memory in CD4(+)-T-cell-deficient mice

Abstract

The primary influenza A virus-specific CD8(+)-T-cell responses measured by tetramer staining of spleen, lymph node, and bronchoalveolar lavage (BAL) lymphocyte populations were similar in magnitude for conventional I-A(b+/+) and CD4(+)-T-cell-deficient I-A(b-/-) mice. Comparable levels of virus-specific cytotoxic-T-lymphocyte activity were detected in the inflammatory exudate recovered by BAL following challenge. However, both the size of the memory T-cell pool and the magnitude of the recall response in the lymphoid tissues (but not the BAL specimens) were significantly diminished in mice lacking the CD4(+) subset. Also, the rate of virus elimination from the infected respiratory tract slowed at low virus loads following challenge of naïve and previously immunized I-A(b-/-) mice. Thus, though the capacity to mediate the CD8(+)-T-cell effector function is broadly preserved in the absence of concurrent CD4(+)-T-cell help, both the maintenance and recall of memory are compromised and the clearance of residual virus is delayed. These findings are consistent with mathematical models that predict virus-host dynamics in this, and other, models of infection.

FIG. 1.

Lung virus titers following primary (A) or secondary (B) challenge of I-A^b+/+ and I-A^b−/− mice. Naïve (A) or PR8-primed (10^8.5 EID₅₀ i.p. 6 weeks earlier) (B) mice were given 10^6.8 EID₅₀ i.n. and sampled at the intervals shown. Log₁₀ dilutions of lung homogenate were used to infect embryonated chicken eggs, and endpoint titrations were determined by a hemagglutination inhibition assay of allantoic fluid. The data are expressed as means ± standard deviations (SD) for groups of five mice each. No virus was recovered from five naïve I-A^b−/− mice sampled at 19 days after infection with the HKx31 virus strain.

FIG. 2.

Peptide-specific CTL activity in the inflammatory cell population recovered by BAL of the infected respiratory tract following secondary i.n. challenge with the HK31 influenza A virus 8 days earlier (see the legend for Fig. 1). The EL4 (H2^b) target cells were pulsed with either the NP₃₆₆ or the PA₂₂₄ peptide prior to use in a standard 6-h ⁵¹Cr release assay. Lytic activities were calculated for the CD8⁺ D^bNP₃₆₆⁺ and CD8⁺ D^bPA₂₂₄⁺ tetramers as determined by tetramer staining (data not shown).

FIG. 3.

Kinetic analysis of the D^bNP₃₆₆ and D^bPA₂₂₄ epitope-specific CD8⁺-T-cell response in I-A^b+/+ and I-A^b−/− mice following primary i.n. challenge with the HKx31 influenza virus. Enriched spleen (A and B), MLN (C and D), and BAL (E and F) samples were stained with anti-CD8 antibody and either the D^bNP₃₆₆ or the D^bPA₂₂₄ tetramer. Each data point represents the mean ± SD of values for the spleen samples and pooled MLN and BAL samples for five mice. Similar results were obtained from two further experiments.

FIG. 4.

Secondary D^bNP₃₆₆ and D^bPA₂₂₄ epitope-specific CD8⁺-T-cell responses in the spleen (A and B), MLN (C and D), and BAL (E and F) samples from I-A^b+/+ (A, C, and E) and I-A^b−/− (B, D, and F) mice. The mice had been primed i.p. with the PR8 virus 6 weeks before i.n. challenge with the HKx31 virus. Each data point represents the mean ± SD of values for the spleen samples and pooled MLN and BAL samples for five mice. Similar results were obtained from two further experiments.

FIG. 5.

Simulation of infection in I-A^b+/+ and I-A^b−/− hosts according to the mathematical model discussed herein. It is assumed that the I-A^b−/− mice lacking help from CD4⁺ T cells differ from the I-A^b+/+ controls in two parameters: the rate of expansion (A) and the life span (B) of their CTLs. Both simulations predict similar dynamics. The infection is resolved less efficiently in I-A^b−/− mice than in I-A^b+/+ mice. At the same time, the CTL dynamics are similar in the presence and absence of T-cell help. The chosen values of parameters were as follows: λ was 10; d was 0.1; β was 0.08; a was 0.2; and p was 1. (A) c equals 0.1 in wild-type hosts and 0.05 in mutant hosts; (B) b equals 0.01 in wild-type hosts and 0.1 in mutant hosts.