use camelcase in angular and asp.net web api json

example here =>

namespace DirectoryApi
{
    public class Directory
    {
        public int Id { get; set; }
        public string FirstName { get; set; } 
        public string LastName { get; set; } 
        public string Telephone { get; set; }
    }
}

you can use FirstName but json returns "firstName". if you use it like this =>

*ngFor <li *ngFor="let directory of directories">
      {{ directory.FirstName }}  {{ directory.LastName }} - {{ directory.Telephone }} - <span>Naber</span>
    </li>

this doesnt work but
this work firstName , lastName ,telephone