Specific decrease of Th1-like activity in mice with plasma cell tumors

Previously we examined the ability of the host's immune responsesto regulate Ig production in an IgE-secreting murine plasmacell tumor (B53). In the present study we have examined thereverse phenomenon, in that we have investigated the effectsof this and other plasma cell tumors on the immune responsesof their hosts. We found that splenocytes from plasma cell tumor-bearingmice demonstrate decreased proliferation in response to polyclonalstimulation by either Con A or a combination of PMA and calciumionophore (A23187[GenBank]). Fractionation of the splenocytes demonstratedthat this reduction in proliferation was confined to CD4⁺T cellsand that the proliferation of CD8⁺ T cells was unaffected. Inorder to determine whether the down-modulatory effects of thetumor were confined to a particular CD4⁺helper T cell subset,we examined the production of cytokines representing the T_h1subset (IL-2 and IFN-) and the T_h2 subset (IL-4 and IL-10) fromstimulated splenocytes and from stimulated enriched splenicT cells. We found that both stimulated splenocytes and T cellsfrom plasma cell tumor-bearing mice produced lower levels ofthe T_h1 cytokines IL-2 and IFN- compared with normal cultures,demonstrating that T_h1-like responses are inhibitsed in thehosts of these tumors. However, no alterations in the productionof the T_h2 cytokines IL-4 and IL-10 were observed in these stimulatedsplenocyte or T cell cultures from the tumor-bearing mice. Thus,our data demonstrate that plasma cell tumors induce a decreasein the immune responsiveness of their hosts, and this decreaseis restricted specifically to T_h1-like activity, with the T_h2-likeactivity and CD8⁺T cell proliferative responses remaining intact.