Shifts in bovine CD4+ subpopulations increase T-helper-2 compared with T-helper-1 effector cells during the postpartum period.

This study determined the cytokine profile of CD4+ T-helper cells to elucidate the specific CD4+ T-helper phenotype during the postpartum period. Peripheral blood mononuclear cells were isolated from cows during periods of increased susceptibility (3 d postpartum, n = 7) and decreased susceptibility (mid- to late lactation, n = 6) to mastitis. Isolated mononuclear cells were magnetically separated into CD4(+)-enriched or CD4(+)-depleted populations using specific bovine monoclonal antibodies and were confirmed to be enriched or depleted by flow cytometric analysis. T-helper-1 and T-helper-2 subpopulations were distinguished by cytokine profiles, at both the molecular and protein level, by competitive quantitative reverse transcriptase-polymerase chain reaction and specific bioassays, respectively. The CD4(+)-enriched cultures isolated postpartum had enhanced interleukin-4 and interleukin-10 mRNA transcript expression; cultures isolated during the mid- to late lactating period had enhanced interleukin-2 mRNA transcripts. Depletion of CD4+ lymphocytes decreased, and enrichment of CD4+ lymphocytes increased interferon-gamma transcripts in cultures isolated from mid- to late lactation cows. Interferon-gamma and interleukin-2 bioassays revealed that cytokine secretion paralleled mRNA transcript levels. These data suggest that CD4+ lymphocytes act predominantly as T-helper-2 compared with T-helper-1 within 3 d after calving. Alterations in the T-helper-1 and T-helper-2 responses, and therefore the repertoire of cytokines produced, may be an underlying reason for diminished host immune response during the postpartum period.