EXPANSION OF A NOVEL PULMONARY CD3(-)CD4(-POPULATION IN MICE DURING CHLAMYDIA-PNEUMONIAE INFECTION() CD8(+) CELL)

A new pulmonary T-cell-like lymphocyte population with the phenotype C D3(-) CD4(+) CD8(+) was discovered in mice. CD4(+) CD8(+) but CD3(+) c ells among murine intestinal intraepithelial lymphocytes have previous ly been described. We describe herein a dramatic expansion of the CD3( -) CD4(+) CD8(+) cell population in response to experimental respirato ry infection. After intranasal Chlamydia pneumoniae infection, CD3(+) CD8(+) cells became transiently the dominant lymphocyte type (maximum of 87% of all lymphocytes) in the lungs of NIH/S mice but remained vir tually undetectable in spleen and blood. The enrichment of these cells was not a C. pneumoniae-specific event, since infection of NIH/S mice with influenza A virus also resulted in an increase in the number of CD4(+) CD8(+) cells (maximum of 42% of all lymphocytes). In addition t o outbred NIH/S mice, two other mouse strains were studied: BALB/c (H- 2(d)) and C57BL/6 (H-2(b)). C. pneumoniae-infected BALB/c mice respond ed with an intermediate increase in the number of CD4(+) CD8(+) cells in lungs, whereas C57BL/6 mice did not respond. The double-positive CD 4(+) CD8(+) cells lacked a major part of the T-cell receptor complex, being both CD3(-) and TCR alpha beta(-). However, when they were stimu lated in vitro with a T-cell mitogen, they responded by proliferation but did not secrete gamma interferon, The dramatic expansion of this c ell population at the infection site suggests an active role for them in respiratory infection, but the specification of this requires furth er study.