**3. Many critical bovine pathogens induce Th0 responses**

In cattle, mixed Th1/Th2 cytokines (both IFNγ and IL-4) have been detected in cultured PBMCs, or Draining Lymph Nodes (DLNs), or local tissues in large number of diseases. Most researchers commonly refer to this as the bovine Th0 response, which may include clones of all three types (Th1, Th2, and Th0) [128, 139–141]. It is important to note that while Th0 clones can produce both IFN γ and IL-4, Th1 and Th2 clones can only produce a single cytokine, either IFN γ or IL-4 (**Figure 4**). Therefore, a mixed population of Th1, Th2, and Th0 cells possibly contributes to the induction of Th0 responses in most of the bovine diseases as explained in Section 4.

### **Figure 4.**

*Helper T cell responses to infections in cattle. Pathogen infections in cattle may induce three types of CD4+ T cell responses: Th1, Th2 and Th0. Th1 responses are characterized by Th1 clones that produce IFN*γ*, Th2 responses include Th2 clones that produce IL-4, and Th0 response could induce mixed populations of clones: Th1, Th2 and Th0. Th0 clones co-express both IFN*γ *and IL-4.*
