Conti A, et al. Molecular characterization and allergenic activity of Lyc e 2 (beta-fructofuranosidase), a glycosylated allergen of tomato. Eur J Biochem 2003;270:1327-37. 5. Lorenz Y, Enrique E, Lequynh L, Fotisch K, Retzek M, Biemelt S, et al. Skin prick tests reveal stable and heritable reduction of allergenic potency of gene-silenced tomato fruits.The human polysaccharide-and protein-specific immune response to Streptococcus pneumoniae is dependent on CD4 1 T lymphocytes, CD14 1 monocytes, and the CD40-CD40 ligand interactionTo the Editor: Streptococcus pneumoniae is a major cause of pneumonia, septicemia, and meningitis. It causes great morbidity and mortality throughout the world. In particular, young children, the elderly, and immunocompromised individuals are susceptible to pneumococcal infections. Host protection against pneumococcal infections is mediated by antibodies against pneumococcal surface proteins and capsular polysaccharides (caps-PSs). 1 Caps-PSs are a main determinant of virulence of S pneumoniae, and antibodies to caps-PSs are protective against infection with S pneumoniae. Some pneumococcal surface proteins, such as pneumococcal surface protein A (PspA), are also considered virulence factors.Whereas proteins are T lymphocyte-dependent antigens, caps-PSs are considered T lymphocyte-independent type 2 (TI-2) antigens. Although T lymphocytes are not needed for induction of the antibody response to TI-2 antigens, they are involved in the regulation of this antibody response. 2 The role of T lymphocytes in the regulation of the antibody production to TI-2 antigens is poorly understood. Little is known regarding the mechanisms by which intact S pneumoniae elicits protein-and caps-PS-specific antibodies in human subjects. In the present study we immunized humanized mice with severe combined immunodeficiency (SCID) with heat-inactivated S pneumoniae as a model to study the human antibody response to S pneumoniae.To evaluate the role of CD4 1 T cells in the antibody response to pneumococcal caps-PSs and PspA, 6-to 8-week-old SCID mice were treated with TMb1 (an anti-murine IL-2 receptor b-chain antibody used to deplete murine natural killer cells and to improve transplant survival 3 ) and transplanted (in peritoneum) either with PBMCs (containing 4 3 10 6 B lymphocytes, n 5 6) or with PBMCs depleted of CD4 1 cells (by using microbeads; Miltenyi Biotec, Bergisch Gladbach, Germany; n 5 6). After transplantation, the mice were immunized with heat-inactivated S pneumoniae serotype 3 (2 3 10 8 colony-forming units). Two weeks after immunization, antibodies were measured by means of ELISA (with preabsorption of the sera with caps-PS serotype 22F [5 mg/L] for anti-caps-PS). 4,5 SCID/SCID mice reconstituted with PBMCs, but not with PBMCs depleted of CD4 1 cells, produced high levels of IgM and IgG antibodies against caps-PSs and PspA (data not shown; P < .03, Mann-Whitney U test).