1. Runtime Environment: Helidon is a lightweight Java microservices framework that provides a simple, functional and reactive programming model for building microservices. On the other hand, Istio is a service mesh platform that helps to connect, secure, and manage microservices. While Helidon focuses on providing a framework for developing microservices, Istio is more focused on managing the communication between microservices in a distributed system.

2. Support for Microservices Communication: Helidon provides support for building microservices using Java programming language, but it does not provide built-in features for handling service-to-service communication, load balancing, and routing. Meanwhile, Istio offers advanced features for managing microservices communication such as traffic routing, load balancing, service discovery, and fault tolerance. Istio uses a data plane and control plane architecture to provide these features.

3. Integration with Kubernetes: Helidon can be deployed and run on Kubernetes, but it does not offer built-in integration with Kubernetes features such as automatic scaling, rolling updates, and service discovery. In contrast, Istio is designed to work seamlessly with Kubernetes and complements its features by providing advanced networking, security, and monitoring capabilities for microservices running on Kubernetes clusters.

4. Service Proxy: In Helidon, service-to-service communication is typically implemented using HTTP clients and servers within the microservices. In Istio, a sidecar proxy is deployed alongside each microservice instance to handle communication, routing, and monitoring at the network level. This proxy intercepts and controls all inbound and outbound traffic to the microservice, providing additional security and observability features.

5. Traffic Management: Helidon does not include built-in tools for advanced traffic management such as A/B testing, canary deployments, and traffic shifting. In contrast, Istio provides powerful traffic management capabilities through its control plane, enabling developers to implement sophisticated deployment strategies and fine-grained routing rules without modifying application code.

6. Security Features: Helidon offers basic security features such as TLS support and authentication mechanisms for securing microservices. On the other hand, Istio provides a robust set of security features including mutual TLS, access control policies, and encryption of service-to-service communication. Istio's security features are configurable and can be applied uniformly across all microservices in the mesh.

In Summary, Helidon is a lightweight Java microservices framework focused on building microservices, while Istio is a service mesh platform that specializes in managing microservices communication, integration with Kubernetes, service proxying, traffic management, and security features for microservices.